000

Evolution of Herbivory in a Carnivorous Clade of (Teleostei: ): Effects on Gut Size and Digestive Physiology

Donovan P. German1,* that the evolution of amylase and chitinase activities was cor- Brett C. Nagle2 related with the evolution of diet in these species, whereas Jennette M. Villeda1 trypsin and lipase activities showed no pattern associated with Ana M. Ruiz1 diet or phylogenetic history. Concentrations of short-chain fatty Alfred W. Thomson1,3 acids were low in all taxa, indicating that these fishes rely largely Salvador Contreras Balderas4,† on endogenous digestive mechanisms to subsist on their re- David H. Evans1 spective diets. Subtle differences in tooth shape were observed 1Department of Biology, University of Florida, Gainesville, between species in the two genera. Overall, our results suggest Florida 32611; 2Bell Museum of Natural History, University that dietary specialization can be observed on the level of anat- of Minnesota, Minneapolis, Minnesota 55108; 3Florida omy and physiology of the digestive tracts of fishes but that Museum of Natural History, University of Florida, such differences are most appropriately viewed in comparisons Gainesville, Florida 32611; 4J. Solis 1504, Colonia La of closely related species with different diets. Nogalera, San Nicolas, Nuevo Leon 66417, Mexico

Accepted 3/22/2009; Electronically Published 11/24/2009 Introduction Online enhancement: appendix. An ’s digestive tract and its associated organs can account for up to 40% of the animal’s metabolic rate (Cant et al. 2006), and because of these costs, the digestive tract must be tightly ABSTRACT regulated in relation to food intake and quality (Karasov and We constructed a phylogeny for 10 species (family Martı´nez del Rio 2007). Thus, an animal’s gut capacity, in terms Cyprinidae) previously revealed to be members of sister genera of size and physiology, should maximize digestion from its with different dietary affinities and used the phylogeny to ex- natural diet; that is, dietary specialization should exist not only amine whether the evolution of digestive tract size and phys- on the level of the community but also on the levels of gut size iology is correlated with the evolution of diet in these fishes. and digestive physiology (Whelan et al. 2000). Accordingly, We studied a total of 11 taxa: four herbivorous species in the many studies of digestion in natural fish populations have fo- Campostoma and six largely carnivorous species in the cused on comparing gut size and digestive enzyme activities genus , including two populations of Nocomis lepto- among herbivores and carnivores in an attempt to identify cephalus, the carnivorous Chattahoochee River drainage pop- specializations of the digestive tract for different diets. A few ulation and the herbivorous Altamaha River drainage popu- interesting patterns have emerged from these investigations. lation. Thus, we were able to compare digestive tract size and First, herbivorous fishes tend to have longer digestive tracts physiology among sister genera (Campostoma and Nocomis) than carnivorous fishes (Al-Hussaini 1947; Zihler 1982; Ribble and among sister taxa (N. leptocephalus Chattahoochee and N. and Smith 1983; Kramer and Bryant 1995; Elliott and Bellwood leptocephalus Altamaha) in dietary and phylogenetic contexts. 2003; German and Horn 2006; Horn et al. 2006). Herbivores The herbivorous taxa had longer digestive tracts and higher presumably have longer guts to allow for higher intake of a activity of the carbohydrases amylase and laminarinase in their low-quality food and to maintain some minimum retention guts, whereas the carnivorous species had higher chitinase ac- time of food in the gut (Ribble and Smith 1983; Sibly and tivity. Phylogenetic independent-contrast analysis suggested Calow 1986; Horn 1989; Starck 2005), thereby increasing di- gestive efficiency (Clements and Raubenheimer 2006). Second, * Corresponding author. Present address: Department of Ecology and Evolu- herbivores consume more carbohydrates than carnivores, and tionary Biology, University of California, Irvine, California 92697; e-mail: hence, carbohydrate-degrading enzymes (e.g., amylase, a- [email protected]. glucanase) tend to be higher in activity in the guts of herbiv- † Deceased. orous fishes than in those of carnivores (Fish 1960; Cockson

Physiological and Biochemical Zoology 83(1):000–000. 2010. ᭧ 2009 by The and Bourne 1972; Reimer 1982; Sabapathy and Teo 1993; Hi- University of Chicago. All rights reserved. 1522-2152/2010/8301-8214$15.00 dalgo et al. 1999; Fernandez et al. 2001; Horn et al. 2006). DOI: 10.1086/648510 In the context of nutrient acquisition matching dietary nu- 000 German, Nagle, Villeda, Ruiz, Thomson, Contreras Balderas, and Evans trient content, also known as the “adaptive-modulation hy- tracts. However, few investigations have examined the concen- pothesis” (summarized in Karasov and Martı´nez del Rio 2007), tration of fermentation end products (SCFAs) in freshwater it is logical that would efficiently digest the nutrients fish species (Smith et al. 1996) to ascertain whether they also most available to them in their food. However, most of the use microbial endosymbionts to digest their food. Furthermore, comparisons of gut size and digestive enzyme activities in fishes we know of none that have examined levels of fermentation (and vertebrates in general) have emphasized completely un- in a phylogenetic context, comparing SCFA concentrations related taxa and were likely confounded by phylogenetic dis- among closely related herbivores and carnivores to observe tance among the species studied. Thus, better phylogenetic con- whether there is dietary specialization in this facet of digestion. trol in comparative studies of digestion has been called for on North American minnows offer an array of feeding modes in several occasions (Karasov and Hume 1997; Horn et al. 2006; which to study digestion in relation to dietary specialization and Karasov and Martı´nez del Rio 2007). evolutionary history. The deeper North American minnow phy- Perhaps not surprisingly, recent investigations have shown that logeny (Simons et al. 2003) comprises primarily carnivorous spe- the phylogenetic history of an animal can have meaningful effects cies, but herbivory is observed in some derived taxa, providing on its gut size and digestive enzyme activities and can result in ample opportunity to investigate the effects of evolution on gut comparative data that conflict with the adaptive-modulation hy- size and digestive physiology. In this study, we examined gut size, pothesis. Elliott and Bellwood (2003) illustrated that gut size digestive enzyme activities, and gastrointestinal fermentation in corrected for body size correlates with diet (i.e., gut lengths fol- sister clades (Simons et al. 2003) of minnows that share a com- lowed the pattern carnivores ! omnivores ! herbivores) in fishes, mon carnivorous ancestor but have evolved different dietary spe- but only within particular fish families. Comparisons of gut cializations (Fig. 1): members of the genus Campostoma are her- length among species in different families did not necessarily bivorous, feeding on algae, diatoms, and detritus (Kraatz 1923; show a correlation with diet. Similarly, German and Horn (2006) Burr 1976; Evans-White et al. 2001; Boschung and Mayden showed that the carnivorous prickleback fish Xiphister atropur- 2004), whereas members of the genus Nocomis are generally car- pureus had body-size-corrected gut lengths that were more sim- nivorous, feeding largely on insects (Lachner 1950; Gatz 1981; ilar to those of its sister taxon, the herbivorous Xiphister mucosus, McNeely 1987; Cloe et al. 1995). than to those of another carnivore, Anoplarchus purpurescens. We chose to construct a phylogeny and measure gut size and The authors argued that X. atropurpureus was constrained by its digestive physiology in 10 species representing the two clades phylogenetic history to have a longer gut despite having a car- (Fig. 1; Table 1): four recognized species of Campostoma and nivorous diet and presumably lower intake than its congener. In six species of Nocomis, including two populations of Nocomis further support of this phylogenetic constraint, Chan et al. (2004) leptocephalus that have different diets, depending on the river and German et al. (2004) found that X. atropurpureus, similar drainage in which they are found—populations of N. lepto- to X. mucosus, had higher activity levels of amylase (a carbo- cephalus from the Chattahoochee River drainage are carnivo- hydrase) in their digestive tracts than did another herbivorous rous, whereas populations from the Altamaha River drainage prickleback, Cebidichthys violaceus. These findings suggest that are herbivorous (D. P. German, personal observation). Thus, phylogenetic relationships among taxa must be taken into ac- we were able to examine characters of gut structure and func- count in studies of gut size and digestive physiology in fishes, tion in sister clades of fishes with different diets (Campostoma especially if dietary specialization is being examined. Although and Nocomis) and in sister taxa with divergent diets (N. lep- some recent studies have investigated gut length and digestive tocephalus Chattahoochee and N. leptocephalus Altamaha). enzyme activities in closely related fish species with different diets Our study had six components relating to food processing and (Chakrabarti et al. 1995; Hidalgo et al. 1999; Horn et al. 2006), digestion in the minnow taxa. First, we analyzed the diets of the to our knowledge, no studies have explicitly tested whether the 11 taxa to confirm that during the period of study, the fish had evolution of a digestive physiological trait (e.g., digestive enzyme the dietary affinities reported for them in the literature. Second, activity) is directly correlated with the evolution of diet in fishes. we compared gut length and gut content mass (GCM) as a Such a study has been performed with phyllostomid bats, and function of body size among the fishes to determine whether a dietary effects on digestive enzyme activities were observed in correlation exists between diet, gut size, and intake when phy- these species when phylogeny was controlled for (Schondube et logenetic history is controlled for. Third, we made qualitative al. 2001). comparisons of the shape of the pharyngeal teeth among the two In addition, some marine herbivorous fishes possess micro- genera. Minnows lack jaw teeth altogether but have pharyngeal bial communities in their digestive tracts that ferment algal and teeth with which they can crush and grind ingested food items plant polysaccharides, making the energy in these compounds (Evans and Deubler 1955; Cloe et al. 1995), making them more available to the host fish in the form of short-chain fatty acids digestible (Xie 1999, 2001). Because pharyngeal teeth are im- (SCFAs; Clements 1997; Burr 1998; Mountfort et al. 2002). portant in the digestive processes of carnivorous (Evans and Those fish species with high levels and rates of microbial fer- Deubler 1955) and herbivorous cyprinids (Xie 1999, 2001), a mentation in their guts (e.g., Kyphosus sydneyanus; Mountfort comparison of tooth shape may provide insight into speciali- et al. 2002; Moran et al. 2005; Clements and Raubenheimer zations of teeth for different diets in these fishes. Fourth, we 2006) may meet a considerable amount of their daily energy compared the activity of five digestive enzymes (amylase, lami- budget from the SCFAs produced by microbes in their digestive narinase, chitinase, trypsin, and lipase) among the 11 taxa, with Evolution of Gut Size and Digestive Physiology 000

Figure 1. Phylogenetic hypothesis for the fish taxa used in this study of gut structure and function. The phylogeny was generated with gene sequences for rhodopsin, interphotoreceptor retinol binding protein, and cytochrome b by use of a mixed-model Bayesian approach and the Akaike Information Criterion. Numbers above branches are Bayesian posterior probabilities. The Campostoma species are herbivorous, and the Nocomis taxa are largely carnivorous, with the exception of Nocomis leptocephalus, of which the Chattahoochee River population is carnivorous and the Altamaha River population is herbivorous. the expectation that enzyme activity would correlate with dietary from streams throughout the eastern United States and north- nutrient composition (Table 2; Karasov and Martı´nez del Rio ern Mexico (Table 1); Nocomis biguttatus is the only exception 2007). Fifth, we observed whether the evolution of carbohydrase and was collected in October 2004. Because we used two pop- activity (amylase, laminarinase, and chitinase) was correlated ulations of Nocomis leptocephalus in this investigation, for clar- with the evolution of diet by using independent-contrast analyses ity we would like to differentiate these two taxa by their feeding (Felsenstein 1985). Because of the relatively consistent support habits: the carnivorous Chattahoochee drainage population of in the literature for the adaptive-modulation hypothesis relating this species will be denoted N. leptocephalus-C and the herbiv- to carbohydrase activities (Schondube et al. 2001; Karasov and orous Altamaha drainage population N. leptocephalus-H. Upon Martı´nez del Rio 2007), we expected to find such a correlation. capture, fish were placed in coolers of aerated stream water and Finally, we compared the SCFA concentrations in the gut fluid held until killed (less than 2 h). Fish were killed in buffered of the two genera, predicting a confirmation of the null hy- Ϫ stream water containing MS-222 (1 g L 1), measured (standard pothesis based on the few data sets available for comparison 0.01 ע [mm), and weighed (body mass [BM 1 ע [length [SL (Clements and Choat 1995; Smith et al. 1996). Overall, our in- g). Individual fish were dissected on a chilled (∼4ЊC) cutting vestigation was designed to determine whether digestive tract size board, and guts were removed by cutting at the esophagus and and physiology actually correlate with diet in these cyprinid fishes the anus. The guts were then uncoiled, without stretching, and in an evolutionary context and/or whether phylogenetic history ע can affect digestive tract function, thereby obscuring character- measured (gut length [GL] 1 mm). Because species of Cam- istics of gut size and digestive physiology relating to dietary postoma and Nocomis have slightly different gut morphology specialization. and guts that differ in length (see Fig. A1 in the online edition of Physiological and Biochemical Zoology), digestive tracts from Material and Methods the two genera were processed in slightly different ways. For Fish Capture, Tissue Preparation, and pH Measurements the Campostoma species, the gut was divided into three equal Fish were captured by seine and backpack electroshocker during sections representing the proximal intestine (PI)—including the the summer months (June–August) between 2004 and 2006 liver, the gall bladder, and pancreatic tissue—the midintestine 000 German, Nagle, Villeda, Ruiz, Thomson, Contreras Balderas, and Evans

Table 1: Collection locations for 11 minnow taxa of the genera Campostoma and Nocomis Taxon (N) Collection Location Drainage Latitude Longitude C. anomalum (10) Flint Creek, Arkansas Arkansas River 36Њ46.142ЈN94Њ41.601ЈW C. ornatum (10) Rı´o Santa Isabel, Chihuahua, Mexico Rı´o Conchos 28Њ32.463ЈN 106Њ30.218ЈW C. oligolepis (10) Wedowee Creek, Alabama Tallapoosa River 33Њ18.496ЈN85Њ26.068ЈW C. pauciradii (7)a Hillabahatchee Creek, Georgia Chattahoochee River 33Њ18.632ЈN85Њ11.288ЈW C. pauciradii (4)a Candler Creek, Georgia Altamaha River 34Њ18.697ЈN83Њ39.441ЈW N. asper (7) Flint Creek, Arkansas Arkansas River 36Њ46.142ЈN94Њ41.601ЈW N. biguttatus (4) Grindstone River, Minnesota St. Croix River 46Њ07.450ЈN93Њ00.420ЈW N. micropogon (6) Shoal Creek, Alabama Tennessee River 34Њ57.140ЈN87Њ35.410ЈW N. platyrhynchus (4) South Fork New River, North Carolina Ohio River 36Њ13.150ЈN81Њ38.250ЈW N. raneyi (6) Tar River, North Carolina Tar River 36Њ10.300ЈN78Њ29.470ЈW N. leptocephalus-H (10) Candler Creek, Georgia Altamaha River 34Њ18.697ЈN83Њ39.441ЈW N. leptocephalus-C (6)b Hillabahatchee Creek, Georgia Chattahoochee River 33Њ18.632ЈN85Њ11.288ЈW N. leptocephalus-C (3)b Pink Creek, Georgia Chattahoochee River 33Њ23.154ЈN85Њ03.468ЈW N. leptocephalus-C (3)b Cavender Creek, Georgia Chattahoochee River 33Њ26.971ЈN85Њ01.290ЈW a Because of dietary and morphological similarities, individuals from the two populations of Campostoma pauciradii were pooled for all analyses. b Similarly, individuals from the three Chattahoochee drainage populations of Nocomis leptocephalus were pooled for all analyses.

(MI), and the distal intestine (DI). For the Nocomis species, until just before use in spectrophotometric assays of activities the gut was divided into two sections, the PI representing the of the five digestive enzymes. proximal third of the intestine—including the liver, the gall In June 2005, four individuals each of Campostoma pauciradii bladder, and pancreatic tissue—up to a “bend” that is present and N. leptocephalus-H from Candler Creek, Georgia, were used in all the studied Nocomis taxa (Fig. A1), and the DI the re- to estimate the pH of the gut in the two genera. Upon collec- mainder. Guts were divided differently among the two genera tion, guts from these fish were dissected, removed, and uncoiled because most Nocomis species did not have enough gut tissue as described above, and incisions were made in the gut wall of to further divide the intestine and allow for tissue homogenates the PI, the MI, and the DI (PI and DI for N. leptocephalus). to be made at a reasonable (!#100) dilution. Once the guts The intestinal tissue of each region was gently squeezed with were measured and divided, the contents of each section were forceps to force contents through the incision. We then dipped squeezed from the gut with the blunt side of a razor blade into pH paper (ColorpHast indicator sticks; MCB Reagents, Gibbs- sterile centrifuge vials. The vials containing these gut contents town, NJ) into the gut contents and estimated pH to the nearest were then capped and immediately frozen, and the remaining 0.5 units. Handling of fish from capture to kill was conducted gut tissues were individually placed in sterile centrifuge vials under approved protocol E006 of the Institutional Animal Care and frozen. The gut contents and tissues were then stored at and Use Committee at the University of Florida. Ϫ80ЊC until analyzed. ע Gut tissues were defrosted, weighed (regional gut mass Phylogenetic Analysis 0.001 g), and homogenized individually in ice-cold 0.05 M Tris- HCl buffer, pH 7.4, with a Polytron homogenizer (Brinkmann A phylogenetic hypothesis of the relationships among species Instruments, Westbury, NY) using a 7-mm generator at 2,200 used in this study was determined through a larger phylogenetic rpm for3 # 30 s (German et al. 2004). Dilution varied between analysis of Nocomis and Campostoma taxa (B. C. Nagle, un- 3 and 100 volumes (v/w), depending on the mass of the gut published data). The phylogenetic study employed sequences region being homogenized. The homogenates were then cen- of the single-copy, protein-coding nuclear markers rhodopsin trifuged at 9,400 g for 2 min at 4ЊC, and the supernatants were and interphotoreceptor retinol binding protein and the mito- collected and stored in small aliquots (100–200 mL) at Ϫ80ЊC chondrially encoded cytochrome b gene from 117 individuals

Table 2: Digestive enzymes assayed in North American minnows Digestive Enzyme Substrate Substrate Source Enzyme Hypothesisa Amylase (a-glucanase) Starch, a(1r4)-glucans Green algae, microbes Elevated in herbivores Laminarinase Laminarin Diatoms Elevated in herbivores Chitinase Chitin Insect exoskeletons, fungi Elevated in carnivores Trypsin Protein Animal, plant, microbial material Elevated in carnivores Lipase Lipid Animal, plant, microbial material Elevated in carnivores a Hypotheses based on the adaptive-modulation hypothesis that enzyme activities will be elevated in the digestive tracts of animals consuming higher concentrations of substrates for particular enzymes (Karasov and Martı´nez del Rio 2007). Evolution of Gut Size and Digestive Physiology 000 of Nocomis and Campostoma collected from across their geo- method (Nelson 1944; Somogyi 1952) as described by German graphic ranges. We also included multiple cyprinid outgroup et al. (2004). Briefly, starch substrate was prepared by boiling taxa in the larger analysis. DNA extraction and PCR amplifi- 2% soluble starch in 0.8 M sodium citrate buffer (pH 7.0) for cation protocols followed Berendzen et al. (2003). This larger 5 min. In a microcentrifuge vial, 50 mL of the starch solution hypothesis of relationships was generated with a mixed-model, was combined with 50 mL of a mixture of sodium citrate buffer partitioned Bayesian method as implemented in the software and gut tissue homogenate. Homogenate volumes ranged from package MRBAYES, version 3.1.2 (Huelsenbeck and Ronquist 5to25mL, depending on a-amylase concentration in the ho- 2001). The best-fitting models of DNA sequence evolution were mogenates. The incubation was stopped after 15–25 min by determined with the Akaike Information Criterion (AIC) in adding 20 mL of 1 M NaOH and 200 mL of Somogyi-Nelson the program MrModeltest (Nylander 2004). Ten million gen- reagent A. Somogyi-Nelson reagent B was added after the assay erations of Markov chain Monte Carlo were performed with a solution was boiled for 10 min (see German et al. 2004 for random starting topology and trees sampled every 100 gen- reagent recipes). The resulting solution was diluted in water erations. A plot of log-likelihood scores of sampled trees against and centrifuged at 6,000 g for 5 min. The glucose content of generation time was produced, and all samples taken before a the solution was then determined spectrophotometrically at 650 stationary likelihood value were discarded as burn-in. The re- nm. The amylolytic activity was determined from a glucose tained trees were used to construct a 50% majority-rule con- standard curve and expressed in U (1 mmol glucose liberated sensus tree. The percentage of times that a particular node was minϪ1) per gram wet weight of gut tissue. Blanks consisting of recovered in the analysis is interpreted as the posterior prob- substrate only and homogenate only (in buffer) were conducted ability of the occurrence of that node (Huelsenbeck and Ron- simultaneously to account for any background levels of re- quist 2001). All interspecific nodes in the expanded phylogeny ducing sugar in the substrate or homogenate and to account were strongly supported (posterior probabilities of 95% or for “endogenous” substrate present in the homogenates. greater). The consensus tree from this expanded analysis was Because laminarin is made up of b(1r3)-glucan (Painter pruned to include only individuals taken from localities that 1983), the same Somogyi-Nelson reducing-sugar analysis was were sampled in this study of gut structure and function. used to assay for laminarinase (E.C. 3.2.1.6) activity. The sub- Branch lengths among terminals in the pruned tree were es- strate was prepared by dissolving 0.5% laminarin in 0.8 M timated by using sequence data from these individuals only. sodium citrate buffer (pH 7.0) heated to ∼95ЊC; the solution was allowed to cool before use in assays. In a microcentrifuge vial, 50 mL of the laminarin solution was combined with 20 Gut Dimension Analyses mL of sodium citrate buffer and 30 mL of homogenate. The Two indexes of gut length relative to body size were used to assay was stopped after 2 h, and laminarinase activity was de- make comparisons of gut size among the 11 taxa: relative gut termined as described above for a-amylase. Reaction times for length (RGL p gut length [mm]/SL [mm]) and Zihler’s index a-amylase and laminarinase assays were determined by stop- (ZI p GL [mm]/10 # BM [g]1/3 ; Zihler 1982). These two di- ping a subset (n p 4 individuals per gut region per species) of gestive-somatic indexes have been used successfully in past the reactions at 1, 2, 5, 10, 15, 25, 30, 60, 120, 180, and 240 comparisons of gut size in different fish taxa (Kramer and min. For a-amylase, the reactions were linear for up to 1 h, Bryant 1995; Elliott and Bellwood 2003; German and Horn and laminarinase reactions were linear for up to 4 h. 2006). The ratio of total GCM to BM (GCM/BM) was also Chitinase (E.C. 3.2.1.14) activity was determined by the re- compared among the species to examine the quantity of food lease of N-acetyl-glucosamine (NAG), following Jeuniaux in the gut in the herbivores and carnivores. (1966), as described by Gutowska et al. (2004). Chitin substrate was prepared as a suspension (5 mg mLϪ1) of native chitin (Sigma C9752) in 0.15 M citric acid and 0.3 M Na HPO buffer, Assays of Digestive Enzyme Activity 2 4 pH 7.0. The solution was constantly stirred on a magnetic stir All assays were carried out at 25ЊC in triplicate with the BioRad plate during pipetting to maintain a uniform colloidal mixture. Benchmark Plus microplate spectrophotomer and Falcon flat- In a microcentrifuge vial, 125 mL of this suspension was com- bottom 96-well microplates (Fisher Scientific, Pittsburgh). All bined with 75 mL of deionized water (two replicates) or, for pH values listed for buffers were measured at room temperature another replicate, 75 mLofb-glucosidase (Sigma G4511, 6 U (22ЊC), and all reagents were purchased from Sigma-Aldrich mLϪ1 in deionized water). The reaction was started with the Chemical (St. Louis, MO). All reactions were run at saturating addition of 50 mL of homogenate, and the assay mixture was substrate concentrations as determined for each enzyme with incubated for 2 h under constant shaking. Afterward, the entire gut tissues from the 11 taxa. Each enzyme activity was measured assay mixture (in the microcentrifuge vial) was placed in a in each gut region of each individual fish. These activities were boiling-water bath for 10 min to stop the reaction. After the then totaled for the whole gut and are expressed as total gut vials cooled, the assay mixture was centrifuged at 13,000 g for enzyme activity (Horn et al. 2006). 15 min. The amount of NAG released was then quantified with The ability of the fish to degrade starch (total amylolytic the method of Reissig et al. (1955). In a microcentrifuge vial, activity, which may encompass amylase and a[1r4]-glucanase 125 mL of the supernatant was combined with 25 mL of 0.8 M activity) was measured according to the Somogyi-Nelson potassium tetraborate, pH 9.3, and boiled for 3 min. After 000 German, Nagle, Villeda, Ruiz, Thomson, Contreras Balderas, and Evans cooling, this reaction mixture was combined with 750 mLof Gastrointestinal Fermentation and Gut Content Analyses p-dimethylaminobenzaldehyde (DMAB) solution and incu- bated in a water bath at 37ЊC for 45 min. DMAB solution was Measurements of symbiotic fermentation activity were based prepared directly before use by adding 1.5 g of DMAB to 100 on the methods of Pryor and Bjorndal (2005) and Pryor et al. mL of glacial acetic acid containing 1.25% (v/v) of 12 M HCl. (2006). Fermentation activity was indicated by relative con- After the 45-min incubation, 100 mL of the assay mixture was centrations of SCFAs in the fluid contents of the guts of the pipetted into a microplate, and the NAG concentration of the fish at the time of death. To prepare them for SCFA analysis, mixture was determined spectrophotometrically at 585 nm. The gut content samples from each region of the intestine (PI, MI, chitinase activity was determined from a NAG standard curve and DI for the Campostoma taxa and PI and DI for the species and expressed in U (1 mmol NAG liberated hϪ1) per gram wet of Nocomis) were weighed, thawed, homogenized with a vortex weight of gut tissue. As in the case of a-amylase and laminar- mixer, and centrifuged under refrigeration (4ЊC) at 16,000 g inase, blanks of substrate only and homogenate only (in buffer) for 10 min. The supernatants from each intestinal region were were conducted to account for any background levels of NAG then pipetted into sterile centrifuge vials equipped with a 0.22- in the substrate or homogenate. mm cellulose acetate filter (Costar Spin-X gamma sterilized cen- Trypsin (E.C. 3.4.21.4) activity was assayed with a modified trifuge tube filters, Corning, NY) and centrifuged under re- version of the method designed by Erlanger et al. (1961), as frigeration at 13,000 g for 15 min to remove particles from the described by Gawlicka et al. (2000). The substrate, 2 mM Na- fluid (including bacterial cells). The filtrates were collected for benzoyl-l-arginine-p-nitroanilide hydrochloride (BAPNA), was each intestinal region and frozen until they were analyzed for dissolved in 100 mM tris-HCl buffer (pH 8.0) by heating to SCFA concentrations. The pelleted gut contents were refrozen 95ЊC (Preiser et al. 1975; German et al. 2004). In a microplate, at Ϫ80ЊC until used for dietary analysis. The masses of the gut 95 mL of BAPNA was combined with 5 mL of homogenate, and contents for each intestinal region were added together to cal- .g) for each individual fish 0.001ע) the increase in absorbance was read continuously at 410 nm culate the total GCM for 15 min. Trypsin activity was determined with a p-nitroan- Concentrations of SCFAs in the gut fluid samples were mea- iline standard curve and expressed in U (1 mmol p-nitroaniline sured by gas chromatography. Samples were hand-injected into liberated minϪ1) per gram wet weight of gut tissue. a Shimadzu GC-9AM gas chromatograph equipped with a Lipase (nonspecific bile-salt-activated E.C. 3.1.1.-) activity flame ionization detector (Shimadzu Scientific Instruments, was assayed with a modified version of the method designed Columbia, MD) and a Perkin Elmer LC-100 integrator (Perkin by Iijima et al. (1998). In a microplate, 86 mL of 5.2-mM sodium Elmer, Shelton, CT). Two microliters of each sample were in- cholate dissolved in 250 mM tris-HCl (pH 9.0) was combined jected onto a 2-m-long glass column (3.2 mm i.d.) packed with with 6 mL of homogenate and 2.5 mL of 10-mM 2-methoxy- 10% SP-1000 and 1% H3PO4 on 100/120 Chromosorb W AW ethanol and incubated at room temperature for 15 min to allow (Supelco, Bellefonte, PA). Carrier gas was N2 at a flow rate of for lipase activation by bile salts. The substrate p-nitrophenyl 40 mL minϪ1. Temperatures of the inlet, column, and detector myristate (5.5 mLof20mMp-nitrophenyl myristate dissolved were 180Њ, 155Њ, and 200ЊC, respectively. An external standard in 100% ethanol) was then added, and the increase in absor- containing 100 mg LϪ1 each of acetate, propionate, isobutyrate, bance was read continuously at 405 nm for 15 min. Lipase butyrate, isovalerate, and valerate was used for calibration. The activity was determined with a p-nitrophenol standard curve SCFA concentrations were expressed as millimoles per liter of and expressed in U (1 mmol p-nitrophenol liberated minϪ1) per gut fluid. Overall, we were able to recover enough gut fluid to gram wet weight of gut tissue. measure SCFA concentrations in the guts of all four Campo-

Michaelis-Menten constants (Km) were determined for tryp- stoma species, the two N. leptocephalus populations, N. bigut- sin, amylase, and lipase in the PI region in the 11 taxa to tatus, and Nocomis micropogon. SCFA concentrations were mea- examine possible differences among the species. Differences in sured in the fluids of the PI, the MI, and the DI (PI and DI the Km values for an enzyme can indicate whether the species of Nocomis species) of the eight taxa. The concentrations of are expressing different isoforms of the enzyme of interest each intestinal region were then added together to calculate the

(Vonk and Western 1984; Voet and Voet 1995). The Km for total SCFA concentrations in the fish’s intestines. Because of amylase was determined with starch concentrations ranging their small size, it was impossible to recover regional intestinal from 0.06% to 3%, for trypsin with BAPNA concentrations contents from Campostoma ornatum, and hence, fluid was ex- ranging from 0.13 to 2.0 mM, and for lipase with p-nitrophenol tracted from the contents of the entire digestive tract for this myristate concentrations ranging from 0.05 to 5 mM. We de- species. termined Km values with the Hill equation, Gut contents were analyzed to confirm that the studied taxa were consuming the diets reported for them in the literature, V [S]n but gut content analyses were carried out in different ways, [E] p max ,(1) nnϩ (K m) [S] depending on the diet of the fish. Gut contents from the PI of the four Campostoma species and herbivorous N. leptocephalus where S is substrate and n is the Hill coefficient set to 1, using were suspended in deionized water, vortexed, and pipetted onto least squares nonlinear regression in Kaleidograph (Synergy, clean microscope slides. The contents were viewed at #100, Reading, PA; Brandt and Vickery 1997). and the percentage area of each food type relative to all other Evolution of Gut Size and Digestive Physiology 000 food types present was quantified for five random fields of view Independent-Contrast Analyses (Evans-White et al. 2001) with ImageJ analytical software Associations were observed between carbohydrase (a-amylase, (Abramoff et al. 2004). Five slides were analyzed in this manner laminarinase, and chitinase) activity and percent animal ma- for each individual fish (i.e., 25 images per fish). Carnivorous terial in the diets of the 11 minnow taxa. The extent to which Nocomis PI gut contents were suspended in deionized water, these digestive carbohydrase activities reflect evolutionary spe- poured into a petri dish, and analyzed under a dissecting mi- cialization to diet was examined in the 11 minnow taxa by croscope (equipped with a net reticle,13 mm # 13 mm ) with analyzing the data within a phylogenetic context with inde- a point-contact method described by German and Horn (2006). pendent-contrast analyses (Felsenstein 1985). Phylogenetically It was necessary to analyze the gut contents of the herbivorous independent contrasts of the activities of each carbohydrase and carnivorous species by different methods because of dif- with percent animal material in the diet were generated using ferences in the particle sizes in the guts of the herbivores and COMPARE 4.6b software (Martins 2004). Branch lengths were carnivores. Campostoma have small algal and detrital particles taken directly from the phylogeny generated for this study (Fig. in their guts, whereas Nocomis have discernible invertebrates 1). To confirm that the branch lengths from the phylogeny in theirs. Percent area or point contacts were totaled for each were appropriate, we examined the correlations of the absolute food item in each individual fish and then totaled and expressed values of the standardized independent contrasts with their as a mean percent for each species. The results were expressed standard deviations (Garland et al. 1992; Garland and Dı´az- as proportions of animal, algal, diatom, and detrital material Uriarte 1999). The contrasts and standard deviations of amylase to provide a broad intraspecific and interspecific comparison (r p 0.24 ,P p 0.51 ), laminarinase (r p Ϫ0.09 ,P p 0.80 ), and of diet composition in the 11 taxa. Animal material was clas- chitinase (r p Ϫ0.33 ,P p 0.35 ) were not correlated. Thus, the sified at the order level, algal material represents filamentous phylogenetically independent contrasts were used in linear- green algae and cyanobacteria, and unidentifiable organic ma- regression analyses, where the regression was forced through terial was classified as detritus. the origin, as is required for analyses of independent contrasts (Felsenstein 1985). Scanning Electron Microscopy of Pharyngeal Teeth The fifth ceratobranchials (pharyngeal arches), which contain Results the pharyngeal teeth in minnows (Eastman and Underhill Phylogeny 1973), were removed with forceps from two specimens each of Campostoma anomalum, Campostoma oligolepis, Nocomis asper, The phylogenetic hypothesis for the studied taxa is presented N. leptocephalus-H, and N. leptocephalus-C. The left and right in Figure 1. Statistical support for the sister relationship be- pharyngeal arches from each fish were then submerged in 1 M tween Nocomis and Campostoma, the monophyly of the two NaOH for 72 h to digest any adhering tissue. After the digestion genera, and relationships among species within them was strong period, the arches (with teeth attached) were rinsed in deionized (Bayesian posteriors of 0.98 or greater) in the pruned analyses. water for2 # 1 h and dried in a drying chamber at room temperature for at least 24 h. Once dry, the teeth were mounted Gut Dimensions, pH, and Diets on aluminum stubs and sputter-coated with gold palladium. Teeth were examined with a Hitachi S-4000 FE SEM (Hitachi The general gut shape and size of the two genera are illustrated Instruments, San Jose, CA), and qualitative comparisons of in Figure A1. As guts were dissected from the animals, they tooth shape were made between the two genera and between were examined for ceca or elaborations of any kind. The only the two populations of N. leptocephalus. difference in gut shape between the two genera appears to be the length (see below) and the number of coils, with the Cam- postoma gut coiling at least 12 times around the swim bladder Statistical Analyses and the Nocomis gut folding two or fewer times in the peritoneal Before all significance tests, a Levene’s test for equal variance cavity before reaching the vent. Significant differences in mean was performed to ensure the appropriateness of the data for RGL and ZI were detected among the 11 minnow taxa (Table the analyses. If the data were not normal, they were log trans- 3). Each of the Campostoma species had guts that were longer formed, and normality was confirmed before analysis. All tests relative to body size than any of the Nocomis taxa. Campostoma were run with Minitab statistical software (ver. 13; Minitab, pauciradii and Campostoma anomalum had the longest guts, State College, PA) unless specified otherwise. Interspecific com- followed by Campostoma oligolepis and Campostoma ornatum, parisons of digestive enzyme activity, total gut SCFA concen- in that order. Among the Nocomis taxa, Nocomis leptocephalus- trations, Km, and GCM/BM were made with ANOVA followed H had gut lengths that were significantly longer than those of by a Tukey’s HSD multiple-comparisons test with a family error the other Nocomis taxa, which did not differ from one another rate ofP p 0.05 . Interspecific comparisons of the gut dimen- (Table 3). Significant differences in GCM/BM were also detected sions (RGL and ZI) were made with ANCOVA, with BM as a among the 11 taxa. Campostoma oligolepis and C. pauciradii covariate, followed by Tukey’s HSD test with a family error had more food in their guts than any of the other species, and rate set atP p 0.05 . Nocomis raneyi displayed the lowest GCM. Notably, N. lepto- 000 German, Nagle, Villeda, Ruiz, Thomson, Contreras Balderas, and Evans

Table 3: Interspecific comparisons of body mass (BM), relative gut length (RGL), Zihler’s index (ZI), and gut content mass as a function of body mass (GCM/BM) in 11 minnow taxa Species BM (g) RGL ZI GCM/BM 006C. ע 78E .034. ע 20E 2.76. ע 82C 5.16. ע Campostoma anomalum 12.76 008C. ע 54C .043. ע 14C 12.36. ע 43AB 3.24. ע Campostoma ornatum 4.48 007E. ע 1.31E .088 ע 35E 20.95. ע 1.15E 5.41 ע Campostoma oligolepis 20.88 008D. ע 69D .061. ע 16D 16.04. ע 1.45BC 4.14 ע Campostoma pauciradii 11.13 002BC. ע 55B .021. ע 14B 4.95. ע 3.39CDE 1.33 ע Nocomis biguttatus 13.52 003BC. ע 36A .017. ע 09A 3.40. ע 2.21BC .88 ע Nocomis asper 8.16 005BC. ע 28A .021. ע 07A 3.38. ע 3.97CDE .87 ע Nocomis micropogon 13.21 003BC. ע 37A .023. ע 10A 3.37. ע 47ABCD .89. ע Nocomis platyrhynchus 4.60 002B. ע 13A .011. ע 04A 3.23. ע 2.25DE .84 ע Nocomis leptocephalus-C 14.13 007C. ע 18B .034. ע 05B 6.43. ע 2.55CD 1.66 ע N. leptocephalus-H 9.61 000A. ע 22A .001. ע 06A 4.14. ע 05A 1.05. ע Nocomis raneyi .72 Species: F (df) 7.83 (10, 89) 185.99 (10, 89) 170.56 (10, 89) 12.29 (10, 89) P !.001 !.001 !.001 !.001 BM: F (df) … .02 (1, 78) .02 (1, 78) … P … .890 .891 … SEM (see table 1 for sample sizes). Interspecific comparisons of body mass (BM) and GCM/BM were ע Note. Values are means analyzed with one-way ANOVA and Tukey’s HSD with a family error rate ofP p 0.05 . Interspecific comparisons of gut dimension parameters were analyzed with ANCOVA (with BM as a covariate) and Tukey’s HSD with a family error rate ofP p 0.05 . Values that share a superscript letter within a parameter are not significantly different. cephalus-H had significantly more GCM than did N. lepto- dominated by clams, damsel fly larvae, and fragments of un- cephalus-C (Table 3). identifiable adult insects. Filamentous green algae composed The digestive tracts of C. pauciradii and N. leptocephalus-H the remaining 0.5% of the diet of N. biguttatus. Nocomis asper were nearly neutral in pH in all regions of the gut (Table 4). consumed only animal material (100%), primarily unidentifi- The lack of acidic conditions and the lack of a pyloric sphincter able adult insect parts but also clams, damsel fly and chiron- (Clements and Raubenheimer 2006) in the PI of either species omid larvae, and ostracods. The diet of Nocomis micropogon is consistent with the general finding that cyprinids lack a gastric was more diverse, with animal material (72.9%) consisting of stomach (Kraatz 1924; Hofer et al. 1982; Chakrabarti et al. unidentifiable adult insect parts, caddis flies, and caddis fly 1995). larvae making up the largest proportion and algae and detritus The proportions of detrital, diatomaceous, algal, and animal making up the remainder, at 19.4% and 7.7%, respectively. The material in the gut contents of all 11 taxa are shown in Figure gut contents of Nocomis platyrhynchus were dominated by an- 2. All four species of Campostoma represent true periphyton imal material (93%), mostly unidentifiable adult insect parts feeders, ingesting almost exclusively detritus, diatoms, and al- and caddis fly larvae, and some filamentous green algae (7%). gae. Campostoma pauciradii consumed the highest proportion Individuals of N. leptocephalus-C were mostly carnivorous of detritus (58.7%), C. anomalum the highest proportion of (91.2% animal material), consuming snails, clams, adult and diatoms (38.8%), and C. oligolepis and C. ornatum had similarly larval caddis flies, adult and larval midge flies, and chironomid high proportions of algae in their diets, at 26.0% and 26.6%, larvae as well as some detritus (8.8%). Individuals of N. lep- respectively. Campostoma ornatum also consumed some animal tocephalus-H, on the other hand, had a diet similar to those of material (5.3%), which consisted of chironomid larvae, un- the Campostoma species, dominated by detritus (37.5%), dia- identifiable insect parts, and fish scales. The diet of Nocomis toms (28.4%), and filamentous green algae (33.8%). Only 0.3% biguttatus was almost entirely animal material (99.5%) and was of their diet was animal material, and this was composed of

Table 4: Intestinal pH of Campostoma pauciradii and Nocomis leptocephalus captured from Candler Creek, Georgia Species PI MI DI Whole Gut 04. ע 7.04 13. ע 7.38 13. ע 6.88 13. ע C. pauciradii 6.88 06. ע 6.69 13. ע NA 6.75 13. ע N. leptocephalus 6.63 Note. Gut regions: proximal intestine (PI), medial intestine (MI), and distal intestine (DI). .SEM (N p 4 ). NA p not available ע Values are means Evolution of Gut Size and Digestive Physiology 000

-dis ( 0.026 ע and C. ornatum ( 0.119 ( 0.017 ע anomalum (0.132 played laminarinase activities that were significantly higher than those of all the studied taxa except N. leptocephalus-H -which in turn did not exhibit activity signifi ,( 0.016 ע 0.091) -Cam 0.017 ע cantly higher than that of C. pauciradii ().0.055 -displayed laminarinase ac ( 0.005 ע postoma oligolepis (0.020 tivity that was not different from that of N. biguttatus -N. platy 0.011 ע 0.002N. micropogon (),or 0.018 ע 0.005,() -Nocomis asper, N. raneyi, and N. lep 0.013 ע rhynchus ().0.022 tocephalus-C had no detectable laminarinase activity (Fig. 3). The opposite pattern was apparent for chitinase activities, with the carnivores displaying higher activities of this enzyme (Fig. 3). Nocomis raneyi had the highest chitinase activity but this activity was not significantly higher ,( 3.48 ע 15.33) N. platyrhynchus 3.90 ע than those of N. biguttatus ()or8.64 These two species, in turn, had activity similar .( 2.28 ע 8.68) 0.61 ע 1.56N. micropogon (), 3.21 ע to that of N. asper (),6.49 Nocomis leptocephalus-H .( 1.84 ע and N. leptocephalus-C (6.55 had the lowest chitinase activity of the Nocomis ( 0.37 ע 2.30) taxa and was statistically similar in activity to the herbivorous -C. oli 0.20 ע 0.22C. ornatum (), 1.37 ע Figure 2. Proportions of animal, algal, diatomaceous, and detrital ma- C. anomalum (),1.22 0.29 ע 0.12C. pauciradii (). 1.21 ע terial in the gut contents of the 11 minnow taxa used in this study. golepis (),and1.01 Phylogenetic relationships at base are from Figure 1 and are used as a guide for the relationships among the studied species. Nocomis lep- The patterns for trypsin and lipase activities were much more tocephalus-C is the carnivorous population of this species from the complicated and did not appear to correlate with diet as much Chattahoochee River drainage, whereas N. leptocephalus-H is the her- as the carbohydrase activities appeared to (Fig. 4). Thus, we bivorous population from the Altamaha River drainage. mention only notable activity levels and significant differences. displayed significantly ( 15.21 ע Nocomis platyrhynchus (68.75 unidentifiable insect parts. Nocomis raneyi consumed mostly higher trypsin activity than any of the other 10 taxa, and N. -had the lowest. Individuals of N. lepto ( 1.96 ע animal material (88.8%), consisting of unidentifiable adult in- raneyi (5.49 displayed significantly higher trypsin ( 2.22 ע sect parts and clams, and filamentous green algae and detritus, cephalus-C (17.56 ע at 10.2% and 1%, respectively. activity than individuals of Nocomis leptocephalus-H (7.95 had the highest ( 0.01 ע Campostoma pauciradii ( 0.13 .(1.59 ע Digestive Enzyme Activities lipase activities, and N. leptocephalus-H (0.06 0.01 ) had the -had sig ( 0.01 ע lowest (Fig. 4). Nocomis leptocephalus-C (0.11 Significant differences in carbohydrase (amylolytic, laminari- nificantly higher lipase activity than N. leptocephalus-H. nase, and chitinase) activities were observed among the 11 min- Significant differences were observed in the Km values of now taxa (Fig. 3). The herbivorous species (all four Campo- amylase, trypsin, and lipase among the 11 minnow taxa, but stoma species and N. leptocephalus-H) generally had higher these differences did not match dietary or phylogenetic patterns ע Ϫ1 amylolytic activity (mean U g gut tissue SEM) than the (see Table A1 in the online edition of Physiological and Bio- ע carnivorous Nocomis taxa. Campostoma pauciradii (837.04 chemical Zoology). and C. ornatum ,( 87.80 ע C. oligolepis ( 791.50 ,(90.04 each displayed significantly higher amylolytic ( 71.60 ע 641.81) activity than any of the Nocomis taxa. Campostoma anomalum -displayed significantly higher amylolytic ac ( 55.70 ע 539.75) tivity than all of the Nocomis taxa except N. biguttatus Independent Contrasts ,( 22.94 ע and N. leptocephalus-H ( 418.72 ( 107.35 ע 327.39) which in turn were not significantly different from one another. Nocomis leptocephalus-H had significantly higher amylase ac- There was a negative correlation between the phylogenetically tivity than the remaining Nocomis taxa, and N. biguttatus had independent contrast of amylolytic activity and the contrast for percent animal material in the diet (Fig. 5), but no significant 20.21 ע higher amylolytic activity than N. micropogon (),69.94 -correlation was detected for the contrasts of laminarinase ac ע and N. raneyi ( 97.70 ,( 23.83 ע N. platyrhynchus (125.29 22.88). Each of these three species had significantly lower ac- tivity and diet. There was a strong positive correlation between and N. leptocephalus-C the phylogenetically independent contrast of chitinase activity ( 41.27 ע tivity than N. asper (266.37 .which were not different from one another. and the contrast for percent animal material in the diet (Fig ,( 25.19 ע 184.86) A similar pattern of higher activity in the herbivores was 5). Thus, the evolution of diet and enzyme activity appears to observed for the enzyme laminarinase as well. Campostoma be correlated for amylolytic capacity and chitinase. 000 German, Nagle, Villeda, Ruiz, Thomson, Contreras Balderas, and Evans

ע Figure 3. Amylolytic (A), laminarinase (B), and chitinase (C) activities in the 11 minnow taxa investigated in this study. Values are means SEM. Interspecific comparisons were made among the taxa for each enzyme with ANOVA followed by Tukey’s HSD with a family error rate ofP p 0.05 . Values for a specific enzyme that share a superscript letter are not statistically different. n.d. p not detectable. Phylogenetic relationships among taxa are as in Figure 1.

Gastrointestinal Fermentation centrations were not significantly different from the highest concentrations observed in C. oligolepis (Table 5). Significant differences in intestinal SCFA concentrations were detected among the eight taxa in which we were able to measure Pharyngeal Teeth these concentrations (Table 5). Campostoma oligolepis displayed the highest SCFA concentrations, and C. pauciradii had the Notable differences are apparent in the shape of the pharyngeal lowest. All eight taxa showed at least some capability for mi- teeth between the species in the two genera (Fig. 6). Although crobial fermentation in their digestive tracts, and this was not these genera have the same number of pharyngeal teeth (4) on limited to the more herbivorous species. Nocomis biguttatus each cerratobranchial, their teeth do differ in shape and ori- and N. micropogon, both carnivores, showed the second- and entation: Nocomis species tend to have sharper, more curved third-highest SCFA concentrations, respectively, and these con- teeth, whereas the Campostoma species have flatter, less curved Evolution of Gut Size and Digestive Physiology 000

SEM. Interspecific ע Figure 4. Trypsin (A) and lipase (B) activities in the 11 minnow taxa investigated in this study. Values are means comparisons were made among the taxa for each enzyme with ANOVA followed by Tukey’s HSD with a family error rate ofP p 0.05 . Bars for trypsin that share a superscript letter are not statistically different. The interspecific differences for lipase activity were too complicated to indicate with superscript letters, and thus are not shown. n.m. p not measured. Phylogenetic relationships among taxa are as in s Figure 1. teeth. Despite their dietary differences, N. leptocephalus-C and intestines did not differ between the two genera, nor were they N. leptocephalus-H had qualitatively very similar teeth that were associated with a specific diet. much different from the teeth of the Campostoma species (Fig. The paradigm for fish nutritional ecology has long been that 6). digestive enzyme activities correlate with diet, and many studies have found support for this, especially for carbohydrate- degrading enzymes (Kapoor et al. 1975; Hidalgo et al. 1999; Discussion Fernandez et al. 2001; Moran and Clements 2002; Drewe et al. Overall, the results of this study provide evidence of both di- 2004; German et al. 2004; Horn et al. 2006), although there etary and phylogenetic effects on gut structure and function in are exceptions (e.g., Skea et al. 2005). In the scope of the adap- the 11 minnow taxa, and most of our hypotheses were sup- tive-modulation hypothesis and given the cost of regulating the ported. The four Campostoma species and Nocomis leptoceph- digestive tract (Caviedes-Vidal et al. 2000; Karasov and Mar- alus-H displayed gut lengths and digestive enzyme activities tı´nez del Rio 2007), it is efficient to have high digestive enzyme that largely matched their dietary preferences, but the gut size activities to degrade those compounds most available in the of N. leptocephalus-H appears to be somewhat constrained by diet. In this study, we found clear associations between the its phylogenetic history. Despite the dietary similarity between ability to digest starch and dietary affinity—the more animal this population of N. leptocephalus and the four species of material consumed, the lower the amylolytic activity, even in Campostoma, the former had guts that were much shorter and a phylogenetic context—suggesting that the evolution of her- more similar to the Chattahoochee population of N. lepto- bivory can lead to an increase in amylolytic activity. This may cephalus than to the Campostoma species. Our hypothesis of be adaptive, because starch and a-glucans probably constitute no difference in tooth shape among the genera was rejected an important energy source for the Campostoma and herbiv- because the teeth of Campostoma species are flatter than those orous N. leptocephalus. The material consumed by these taxa of the Nocomis taxa. Also, SCFA concentrations in the minnow is best described as periphyton, or the epilithic algal complex 000 German, Nagle, Villeda, Ruiz, Thomson, Contreras Balderas, and Evans

together. Laminarin is the storage polysaccharide of diatoms and brown algae (Painter 1983), and fishes that consume more laminarin have higher laminarinase activities (Sturmbauer et al. 1992; Moran and Clements 2002; Skea et al. 2005). Sturm- bauer et al. (1992) showed that herbivorous and omnivorous cichlids consuming less of the EAC, and hence fewer diatoms, had no detectable laminarinase activity in their guts whereas EAC-consuming fishes had higher laminarinase activity. How- ever, in accordance with previous studies (Moran and Clements 2002; Skea et al. 2005; German and Bittong 2009), laminarinase activities in the minnows are several orders of magnitude lower than the amylolytic activity, suggesting a lower importance of laminarin to the overall nutrition of the fish. Campostoma anomalum and Campostoma oligolepis con- sumed the most diatoms in this study, yet C. oligolepis had the lowest laminarinase activity among the Campostoma. Individ- uals of C. anomalum have been shown to selectively feed on diatoms in some habitats, even when diatoms are not the most abundant food item (Napolitano et al. 1996). Furthermore, when sympatric, C. anomalum and C. oligolepis have been ob- served to exhibit niche partitioning and feed on different re- sources (Fowler and Taber 1985). Thus, it is possible that species in the clade to which C. anomalum and Campostoma ornatum belong are specialists on diatoms and hence have higher lam- inarinase activity than species in the C. oligolepis–Campostoma pauciradii clade, but this is purely speculative and is not nec- essarily supported by our gut content analyses. The activity of the brush-border disaccharidase maltase also follows the pat- tern of different activity between the two clades (German 2009a) and may reflect some deeper evolutionary and ecological

Table 5: Total short-chain fatty acid (SCFA) concentration (mM) in the digestive tracts of eight minnow species with Figure 5. Relationships between digestive carbohydrase activity and different diets percent animal material in the diet for 11 minnow taxa, plotted as phylogenetically independent contrasts. Regression coefficients are on Species (Diet) N SCFA Concentrationa the graphs. Relationships are considered significant atP p 0.10 . Campostoma anomalum 1.67A ע herbivore) 6 12.96) (EAC), which is a loose assemblage of bacteria, cyanobacteria, Campostoma ornatum filamentous green algae, diatoms, and detritus that grows on 1.55A ע herbivore) 8 9.60) hard substrates (Hoagland et al. 1982; van Dam et al. 2002; Campostoma oligolepis Klock et al. 2007). Starch is the storage polysaccharide of green 2.39B ע herbivore) 10 22.54) algae (Painter 1983), and bacterial and algal mats contain a Campostoma pauciradii large proportion of soluble polysaccharides in exopolymeric 98A. ע herbivore) 7 7.45) substances (Leppard 1995; Wotton 2004; Klock et al. 2007). Nocomis biguttatus Thus, the elevated amylolytic activity in the minnows may be 3.98AB ע carnivore) 3 16.24) a combination of amylase and a general a(1r4)-glucanase Nocomis micropogon (Skea et al. 2005), allowing the fishes to hydrolyze a variety of 2.19AB ע carnivore) 5 14.42) microbial and algal polysaccharides. Indeed, the general re- Nocomis leptocephalus ducing-sugar assay we used to determine amylolytic activity 2.36A ע carnivore) 3 9.60) probably measures amylase and a(1r4)-glucanase, not amylase 2.32A ע N. leptocephalus (herbivore) 10 8.06 alone. ע Laminarinase activity was also clearly more important in the Note. Values are means SEM. Interspecific comparisons of SCFA con- centration were analyzed with one-way ANOVA and Tukey’s HSD with a herbivorous taxa, although this was difficult to observe statis- family error rate ofP p 0.05 . Values that share a superscript letter are not tically because three Nocomis taxa (Nocomis asper, Nocomis ra- significantly different. a p ! neyi, and N. leptocephalus-C) lacked laminarinase activity al- F7,47 6.62,.P 0.01 Evolution of Gut Size and Digestive Physiology 000

Figure 6. SEM micrographs of the pharyngeal teeth of herbivorous Campostoma oligolepis (A), carnivorous Nocomis asper (B), herbivorous Nocomis leptocephalus (C), and carnivorous N. leptocephalus (D). Scale bar p 1 mm. differences between the two parts of the Campostoma phy- minnows—which all possess anatomically unspecialized intes- logeny. tines, albeit of different lengths, and have pharyngeal teeth— To our knowledge, there have been no comparisons of chi- chitinase activity is clearly higher in fishes consuming more tinase activity among herbivorous and carnivorous fishes in a insects and thus more chitin. The higher chitinase activity in phylogenetic context. A dietary effect on chitinase activity in the Nocomis may be adaptive (as indicated in the independent- fish digestive tracts is well known, however. Goodrich and Mo- contrast analyses), although feeding trials would be necessary rita (1977a) found a relationship between diet and chitinase to test this assertion. Because the Nocomis taxa have pharyngeal activity in Enophrys bison and Platyichthys stellatus (more chitin teeth with which to disrupt prey exoskeletons and because chi- in the diet, higher chitinase activity). Danulat (1986) showed tin is composed of a usable energy source for vertebrates (i.e., that Gadus morhua consuming crab and shrimp had higher NAG; Gutowska et al. 2004), chitin may represent an important chitinase activities in their guts than individuals of this same additional source of nitrogen and energy to the Nocomis species. species consuming a fish diet. However, Gutowska et al. (2004) Moreover, these fishes may play a role in chitin degradation in found that chitinase activity in 13 species of marine carnivorous North American freshwater ecosystems (Goodrich and Morita fishes was associated more with intestinal length than with diet: 1977b). fishes with shorter intestines had higher chitinase activity. The No pattern relating to diet has been established for protease authors suggested that this elevated chitinase activity was more activities. In fact, proteolytic enzyme activity in herbivorous likely for the disruption of prey exoskeletons, preventing in- fishes has often been found to be equal to or higher than that testinal blockage, than for the digestion and absorption of NAG in carnivorous fishes (Sabapathy and Teo 1993; Hidalgo et al. from chitin per se. Lindsay (1984) found no relationship be- 1999), even in closely related species (Chan et al. 2004). Hofer tween diet and chitinase activity in 29 species of marine and and Schiemer (1981) argued that because many herbivorous freshwater fishes but suggested that fishes with the ability to fishes have higher intake and more rapid gut throughput than mechanically disrupt prey exoskeletons (e.g., with pharyngeal their carnivorous relatives, they likely have higher daily pro- teeth) had lower chitinase activity than species that do not duction and activity of proteases than carnivores, regardless of mechanically manipulate prey. The findings of Gutowska et al. the “snapshot” protease activities measured at the time of death. (2004) and Lindsay (1984) beg for a comparison of chitinase Given the observation in this study that the herbivorous species activity among closely related fishes with similar gut mor- likely have higher intake (i.e., greater GCM) and thus would phology and ability to mechanically disrupt prey to discern be expected to have more rapid gut transit rates (Sibly and whether a dietary effect on chitinase activity exists. Among the Calow 1986), it is likely that they produce more proteolytic 000 German, Nagle, Villeda, Ruiz, Thomson, Contreras Balderas, and Evans enzymes (and all enzymes, for that matter) than the carnivores ized digestive tract, it makes sense to have an elongated intestine to ensure acquisition of protein from their low-protein diet and most likely an expanded absorptive surface area (German (Hofer and Schiemer 1981; Smoot and Findlay 2000; Chan et 2009b), because such animals pass food through their guts in al. 2004; German and Bittong 2009). In further support of this a rapid fashion (Sibly and Calow 1986; Horn et al. 2006; Kara- contention, N. leptocephalus-C had higher trypsin activity than sov and Martı´nez del Rio 2007; German 2009b). Rapid transit N. leptocephalus-H, but N. leptocephalus-C also had lower GCM of ingesta through the gut means that food passes through each than N. leptocephalus-H. Lower intake can equate to longer region of the intestine only once and is not retained anywhere retention of food in the gut (Sibly and Calow 1986), especially along the gut for any length of time. Thus, it is important to in predators that may experience extended times between meals. expose ingesta to as much absorptive surface as possible (Horn When they actually encounter food, carnivorous Nocomis may et al. 2006; German 2009b). Similarly, N. leptocephalus-H feeds rapidly increase digestive enzyme secretion, which can result on the EAC and has a longer gut than N. leptocephalus-C, but in higher digestive enzyme activity after consumption of a meal it is a gut that is one-half to one-third the length of the Cam- (Cox and Secor 2008), especially in comparison to herbivorous postoma intestines. This is the clearest example of a phylogenetic taxa that constantly have food in their guts. constraint in our data set, and it further illustrates why phy- Another way to examine patterns of protease activity is in logenetic history must be taken into account in comparisons the context of nutrient targets and daily protein requirements of gut size among fishes with different diets (German and Horn (Raubenheimer and Simpson 1998). Many fishes are known to 2006). feed to meet protein requirements, even if excess carbohydrates We hypothesized that there would be no differences in the are consumed in the process (Raubenheimer et al. 2005; Clem- intestinal SCFA concentrations among species of Campostoma ents and Raubenheimer 2006). Thus, if herbivores consuming and Nocomis, and this appears to be true. Species of both genera a low-protein diet are found to exhibit relatively high proteo- have some level of gastrointestinal fermentation in their guts lytic enzyme activities (e.g., loricariid catfishes; German and regardless of diet. Although some marine herbivorous fishes Bittong 2009), this may be due to the fishes scavenging any may meet a large proportion of their daily energy needs via protein they can to meet their daily protein targets, whereas SCFAs produced by endosymbiotic microorganisms (Mount- carnivores have a simpler task of meeting their daily protein fort et al. 2002), this is not necessarily true for all nominally needs with their higher-protein diet. herbivorous fishes, especially for those that consume more de- Like protease activity, lipase activities have often been found tritus (Crossman et al. 2005). The highest SCFA concentrations to be equal among herbivores and carnivores (Horn et al. 2006) observed in this study—22.54 mM SCFA for the whole gut in or actually higher in herbivores (Nayak et al. 2003; German et C. oligolepis—still qualify as “low fermentation potential” al. 2004). Similar to what Hofer and Schiemer (1981) suggested among herbivorous fishes (Choat and Clements 1998), and the for protease activity, German et al. (2004) argued that because second- and third-highest SCFA concentrations in this study an herbivorous diet is lower in lipid than a carnivorous one, were observed in the carnivorous Nocomis biguttatus and No- herbivores attempt to maximize lipid digestion and assimilation comis micropogon. This is consistent with a previous investi- (especially of essential fatty acids) by having higher lipase ac- gation in freshwater fishes that revealed higher SCFA concen- tivities. This counterobservation to the adaptive-modulation trations in the hindgut of carnivorous Micropterus salmoides hypothesis has been seen in vitamin and mineral transport than in omnivorous Cyprinus carpio or detritivorous Dorosoma activity along the intestinal epithelium (Karasov and Hume cepedianum (Smith et al. 1996). Furthermore, the SCFA con- 1997) and may certainly apply to limiting nutrients (and their centrations in the minnow guts are not higher in one region acquisition) across the board. of the intestine than another (i.e., foregut or hindgut; German Cyprinid fishes are known to lack a gastric stomach (Kraatz 2009a), as is commonly the case in animals that rely on gas- 1924; Hofer et al. 1982; Chakrabarti et al. 1995), and our results trointestinal fermentation (Stevens and Hume 1998). Thus, al- support this notion because we measured alkaline conditions though species of Campostoma and Nocomis may meet some throughout the guts of C. pauciradii and N. leptocephalus-H. proportion of their daily energetic needs via gastrointestinal We also found no valves or ceca of any kind, further suggesting fermentation, they likely rely more on endogenous digestive that minnows have anatomically unspecialized digestive tracts mechanisms. that are little more than an intestine from beginning to end. There are clear differences in the shape of the pharyngeal The length of the digestive tract, however, is definitely affected teeth between Campostoma and Nocomis that may be related by diet and evolutionary history. The RGL and ZI of the Cam- to their phylogenetic history and evolution of dietary special- postoma species were two to seven times those of the Nocomis ization. The Nocomis taxa clearly have curved, villiform teeth, species, consistent with many previous observations that her- whereas the Campostoma have flatter, less curved teeth. It is bivorous fishes have longer guts than carnivorous ones (Zihler fitting that the Nocomis would have sharper teeth for piercing 1982; Ribble and Smith 1983; Kramer and Bryant 1995; German and shredding insect exoskeletons, whereas Campostoma have and Horn 2006). Campostoma anomalum and C. oligolepis are flatter teeth that act as a grinding surface to break apart diatom known to feed on the EAC throughout the diel cycle and to tests and algal cell walls. Differences in pharyngeal tooth shape pass food through their intestines in less than 8 h (Fowler and in relation to diet have been observed in cichlids (Hulsey et al. Taber 1985). With high intake and an anatomically unspecial- 2005, 2006). In addition, N. raneyi apparently undergoes an Evolution of Gut Size and Digestive Physiology 000 ontogenetic shift in diet in some locales from one dominated his kindness will be missed. He was a first-rate biologist, father, by insects to one dominated by molluscs, which results in a and human being. strengthening of the pharyngeal teeth in this species; the teeth become more rigid and blunt in larger fish than in smaller fish (Cloe et al. 1995). The lack of difference in pharyngeal tooth Literature Cited shape between the two N. leptocephalus populations, despite their dietary differences, suggests that tooth shape is not nec- Abramoff M., P. Magelhaes, and S. Ram. 2004. Image processing essarily plastic in all Nocomis species and that a specific tooth with ImageJ. Biophotonics Int 11:36–42. shape is not required for a specific diet in these species. Al-Hussaini A.H. 1947. The feeding habits and the morphology In conclusion, this study is one of very few to investigate of the alimentary tract of some teleosts living in the neigh- fish gut structure and function in a phylogenetic context, and bourhood of the marine biological station, Ghardaqa, Red the results are not necessarily surprising: there is a clear as- Sea. Publ Mar Biol Stn Al Ghardaqa 5:1–61. sociation between diet, gut size, and digestive enzyme activities Berendzen P., A. Simons, and R. Wood. 2003. Phylogeography in minnows of the genera Campostoma and Nocomis. However, of the northern hogsucker, Hypentelium nigricans (Teleostei: this is the first study to actually evaluate whether the evolution ): genetic evidence for the existence of the of diet and gut structure and function can be correlated in ancient Teays River. J Biogeogr 30:1139–1152. fishes; they apparently can be in these minnows. We do caution Blum M.J., D.A. Neely, P.M. Harris, and R. Mayden. 2008. that our results do not definitively answer whether the digestive Molecular systematics of the cyprinid genus Campostoma physiology of the minnows is fixed in a manner appropriate (: Cypriniformes): disassociation between for digesting a specific diet. Thus, in many ways our results are morphological and mitochondrial differentiation. Copeia a first step, setting the stage for more complete analyses of the 2008:360–369. digestive physiology of Campostoma and Nocomis in a labo- Boschung H.J. and R. Mayden. 2004. Fishes of Alabama. 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MS thesis. East atomically unspecialized digestive tracts in comparison with Carolina University, Greenville, NC. terrestrial vertebrates, there are subtle differences in the bio- Cant J.P., B.W. McBride, and W.J. Croom Jr. 2006. The regu- chemistry of digestion and gut anatomy that allow for dietary lation of intestinal metabolism and its impact on whole an- specialization. imal energetics. J Anim Sci 74:2541–2553. Caviedes-Vidal E., D. Afik, C. Martı´nez del Rio, and W.H. Karasov. 2000. Dietary modulation of intestinal enzymes of Acknowledgments the house sparrow (Passer domesticus): testing an adaptive hypothesis. Comp Biochem Physiol A 125:11–24. We wish to thank Daniel Neuberger, Coleman Sheehy, Jeremy Chakrabarti I., M.A. Gani, K.K. Chaki, R. Sur, and K.K. Misra. Wright, Ankita Patel, Jacob Egge, Stephanie Boyd, and Kim 1995. Digestive enzymes in 11 freshwater teleost fish species Backer-Kelly for help in the field and in the laboratory. This in relation to food habit and niche segregation. Comp project was funded by an American Museum of Natural History Biochem Physiol A 112:167–177. Theodore Roosevelt Memorial Grant, a University of Florida Chan A.S., M.H. Horn, K.A. Dickson, and A. Gawlicka. 2004. Mentoring Opportunity Program Scholarship, a University of Digestive enzyme activity in carnivores and herbivores: com- Florida Department of Zoology Brian Riewald Memorial Grant, parisons among four closely related prickleback fishes (Tel- and a National Science Foundation (NSF) GK-12 research sti- eostei: Stichaeidae) from a California rocky intertidal habitat. pend (all to D.P.G.); a Dayton-Wilke Memorial Fund for Nat- J Fish Biol 65:848–858. ural History from the James Ford Bell Museum of Natural Choat J.H. and K.D. Clements. 1998. Vertebrate herbivores in History, University of Minnesota (to B.C.N.); NSF grant DEB- marine and terrestrial environments: a nutritional ecology 0315963 (L. M. 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