diversity

Review Effect of on Shaping Parental Brood Defense and Larval Ontogeny of Convict Leading to Population Divergence

Brian D. Wisenden

Biosciences Department, Minnesota State University Moorhead, Moorhead, MN 56563, USA; [email protected]; Tel.: +1-218-477-5001  Received: 7 March 2020; Accepted: 25 March 2020; Published: 2 April 2020 

Abstract: (1) Predation selects for antipredator competence in prey. For fishes with parental care, brood predators exert selection on the morphological phenotype of offspring, and also exert strong selection pressure to promote parental care behavior of adults. (2) This review summarizes field and lab studies on the ontogeny of antipredator competence in convict cichlids, a freshwater fish with extended biparental care of their free-swimming young. (3) Here, data show that differences in swimming performance between small and large young are exploited by parents when they adopt (smaller) young. Velocity and acceleration of startle responses improves nonlinearly with body size, increasing rapidly at a point when the skeleton rapidly ossifies from cartilage to bone, at the size at which discrimination by adopting parents shifts, and the timing of change in the rate of change in area protected by parents. Convict cichlids in a Nicaraguan lake population showed a similar correlation among these traits, but these traits are delayed relative to Costa Rican fish. (4) Population divergence is likely explained by relatively more intense brood predation in the lake, which selects for different optima of larval antipredator competence and parental brood defense.

Keywords: predation; brood predators; parental care; diversification; skeletal ossification; convict

1. Introduction Predation is a major arbiter of natural selection that exerts its effects on prey evolution by pruning variation in behavioral, ontological and morphological phenotypes of prey [1–3]. There are many elegant demonstrations of the effects of predation through comparison of prey populations that occur in sympatry or allopatry with predators [4]. In this paper, I summarize a series of previously published papers on the evolutionary ecology of a freshwater fish , the siquia, that reveal trait divergences in larval swimming performance and parental care between populations exposed to different levels of brood predation. Unlike forms of parental care practiced by birds and mammals, parental fish generally do not provision their young with food. Parental care in fishes is primarily in the form of defense of developing embryos and newly hatched young against the threat of predators. Moreover, because adult fish are several orders of magnitude larger than their young (unlike birds and mammals), predators of fish larvae and young juveniles pose no threat to parents. Therefore, fish are ideal organisms for studying the effects of predation on the evolution of parental care. Parental care itself is linked to the ontogeny of antipredator competence of the young. There is a direct link between the vulnerability of young to predation, the duration and intensity of care, and the allocation of resources to reproduction. vary widely in all of these traits and parental care behavior lies at the nexus of these life-history trade-offs.

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2. Study System 2. Study System Convict cichlids are biparental freshwater fish endemic to , ranging from PanamaConvict to cichlids are [5]. biparental Their taxonomic freshwater classification fish endemic has to Centralbeen revised America, multiple ranging times from in recent toyears Guatemala such that [5 ].the Their common taxonomic name classification“convict cichlid” has beenis more revised useful multiple than the times Latin in recentname. yearsCurrently, such thatconvict the commoncichlids that name occur “convict in Costa cichlid” Rica isand more Nicaragua useful than are theclassified Latin name. as Amatitlania Currently, siquia convict [6,7]. cichlids Most thatof the occur data inpresented here and were Nicaragua collected arein stud classifiedy populations as Amatitlania in clear siquia low-order[6,7]. streams Most of in the Lomas data presentedBarbudal hereBiological were collectedReserve, inGuanacaste, study populations Costa Rica in clear (Figure low-order 1). A streams key comparison in Lomas Barbudal for the Biologicalunderstanding Reserve, of how Guanacaste, predation Costahas shaped Rica (Figure life history1). A traits key comparison comes from for additional the understanding data collected of howin Laguna predation de Xiloá, has shaped a volcanic life history crater traits lake comesin Nicaragua from additional and lab datastudies collected based in on Laguna fish from de Xilo thisá, apopulation. volcanic crater lake in Nicaragua and lab studies based on fish from this population.

Nicaragua

Laguna de Xiloá Costa Rica

Reserva Biológica Lomas Barbudal

Figure 1. Map of Central America indicating the location of Lomas Barbudal Biological Reserve and Laguna de XiloXiloá.á. 3. Mating System of Convict Cichlids in Costa Rican Streams 3. Mating System of Convict Cichlids in Costa Rican Streams Parental care is tied closely to the mating system. Therefore, a discussion of parental care requires Parental care is tied closely to the mating system. Therefore, a discussion of parental care some background information about the mating system. Spawning is seasonal. In Costa Rican streams, requires some background information about the mating system. Spawning is seasonal. In Costa spawning activity peaks in the dry season in March–April (Figure2). The rainy season create spates Rican streams, spawning activity peaks in the dry season in March–April (Figure 2). The rainy season that scour out sediment and organic debris, and create turbid conditions and violent flows unfavorable create spates that scour out sediment and organic debris, and create turbid conditions and violent for maintaining parent–offspring contact. During the dry season these streams are fed by ground water, flows unfavorable for maintaining parent–offspring contact. During the dry season these streams are flow is gentle and stable, and the water is clear. The dry season is also a time when dry forest trees fed by ground water, flow is gentle and stable, and the water is clear. The dry season is also a time drop their leaves, which blow into the stream and create a burst of allochthonous production. Convict when dry forest trees drop their leaves, which blow into the stream and create a burst of cichlids engage in leaf-turning behavior to expose the underside of leaves for their own foraging, and allochthonous production. Convict cichlids engage in leaf-turning behavior to expose the underside when guarding young, they increase leaf turning frequency to provide foraging opportunities for their of leaves for their own foraging, and when guarding young, they increase leaf turning frequency to young [8]. provide foraging opportunities for their young [8]. Convict cichlids form monogamous pair bonds and jointly defend a nest cavity from competing conspecific reproductive80 pairs. Within pairs, males are larger than females and this species shows size-assortative mating (Figure3). Biparental care is uncommon in fishes. For convict cichlids 70 in this study system, biparental care is more effective than uniparental care in defending against brood predators [960], and allows pairs to defend two territories simultaneously: the mobile territory surrounding the brood,50 and the fixed territory around the spawning lair. Brooding adults and their offspring return to40 the lair each night, presumably to take refuge from nocturnal predators such as catfish Rhamdia guatemalensis. During the day, broods roam about the stream bottom foraging on the 30 substrate. About once every 10 min, one parent, usually the male, leaves their partner and young to return to the lairbroods of Number to20 chase away conspecifics that may be looking to establish themselves there. 10 0 1 7 13 19 25 31 37 43 49 55 61 67 73 79 85 91 97 103 109 115 121 127 133 139 145 151 157 163 169 175 Julian Date

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2. Study System Convict cichlids are biparental freshwater fish endemic to Central America, ranging from Panama to Guatemala [5]. Their taxonomic classification has been revised multiple times in recent years such that the common name “convict cichlid” is more useful than the Latin name. Currently, convict cichlids that occur in Costa Rica and Nicaragua are classified as [6,7]. Most of the data presented here were collected in study populations in clear low-order streams in Lomas Barbudal Biological Reserve, Guanacaste, Costa Rica (Figure 1). A key comparison for the understanding of how predation has shaped life history traits comes from additional data collected in Laguna de Xiloá, a volcanic crater lake in Nicaragua and lab studies based on fish from this population.

Nicaragua

Laguna de Xiloá Costa Rica

Reserva Biológica Lomas Barbudal

Figure 1. Map of Central America indicating the location of Lomas Barbudal Biological Reserve and Laguna de Xiloá.

3. Mating System of Convict Cichlids in Costa Rican Streams Parental care is tied closely to the mating system. Therefore, a discussion of parental care requires some background information about the mating system. Spawning is seasonal. In Costa Rican streams, spawning activity peaks in the dry season in March–April (Figure 2). The rainy season create spates that scour out sediment and organic debris, and create turbid conditions and violent flows unfavorable for maintaining parent–offspring contact. During the dry season these streams are fed by ground water, flow is gentle and stable, and the water is clear. The dry season is also a time when dry forest trees drop their leaves, which blow into the stream and create a burst of allochthonous production. Convict cichlids engage in leaf-turning behavior to expose the underside Diversityof2020 leaves, 12, for 136 their own foraging, and when guarding young, they increase leaf turning frequency to3 of 15 provide foraging opportunities for their young [8].

80 Diversity 2020, 12, x FOR PEER REVIEW 3 of 15 70 Figure 2. The number60 of breeding pairs actively guarding broods in the dry seasons of 1990 and 1991 within defined study areas in the Río Cabuyo and its tributary Quebrada Amores, located in and 50 adjacent to Lomas Barbudal Biological Reserve, Guanacaste, Costa Rica. Data from [9]. 40 Convict cichlids30 form monogamous pair bonds and jointly defend a nest cavity from competing conspecific reproductive pairs. Within pairs, males are larger than females and this species shows Number of broods of Number 20 size-assortative mating (Figure 3). Biparental care is uncommon in . For convict cichlids in this study system, biparental10 care is more effective than uniparental care in defending against brood predators [9], and 0allows pairs to defend two territories simultaneously: the mobile territory 1 7 13 19 25 31 37 43 49 55 61 67 73 79 85 91 97

surrounding the brood, and the fixed territory around the spawning103 109 115 121 127 lair.133 139 Brooding145 151 157 163 169 adults175 and their offspring return to the lair each night, presumablyJulian to takeDate refuge from nocturnal predators such as

Figurecatfish 2.RhamdiaThe number guatemalensis of breeding. During pairs the actively day, broods guarding roam broods about inthe the stream dry seasons bottom of foraging 1990 and on 1991 the substrate. About once every 10 min, one parent, usually the male, leaves their partner and young to within defined study areas in the Río Cabuyo and its tributary Quebrada Amores, located in and return to the lair to chase away conspecifics that may be looking to establish themselves there. adjacent to Lomas Barbudal Biological Reserve, Guanacaste, Costa Rica. Data from [9].

AMP90 25 88 1990 1991 CABP90

83 AMS90 20 CABS90

78 AMP91 CABP91 15 73 AMS91 CABS91 68 10

63

Male standard length (mm) length standard Male 5 MSL - (mm) within FSL pairs 58

53 0 33 43 53 63 AmP CabP AmS CabS Female standard length (mm) (a) (b)

FigureFigure 3. (a )3. Male (a) Male standard standard length length (mm) (mm) versus versus female female standard standard length length in matedin mated pairs pairs of convictof convict cichlids by 1990cichlids and by 1991 1990 in and the 1991 pool in (P) the and pool stream (P) and (S)stream habitat (S) habitat in Río in Cabuyo Río Cabu andyo and Quebrada Quebrada Amores. Amores. Large malesLarge monopolize males monopolize spawning spawning sites and sites large and females large producefemales produce larger clutches larger clutches leading leading to size-assortative to size- assortative mating. (b) Overall mean ± SE length difference within a pair was 13.78 ± 0.59 mm (n = mating. (b) Overall mean SE length difference within a pair was 13.78 0.59 mm (n = 149), and 149), and intrapair difference± differed significantly by site (F3,145 = 44.25, p < 0.001).± Small females were intrapair difference differed significantly by site (F = 44.25, p < 0.001). Small females were not not found spawning in Quebrada Amores as often as3,145 they occurred in Río Cabuyo. Data from [10]. found spawning in Quebrada Amores as often as they occurred in Río Cabuyo. Data from [10]. The young emerge from the lair at a size of about 4.5–5.0 mm standard length (SL) and remain Theassociated young with emerge parental from protection the lair at until a size they of aboutare about 4.5–5.0 10 mm mm SL, standard which can length take (SL) 4–6 andweeks remain associateddepending with parentalon the growth protection rate of until fry theythat arevaries about from 10 mmsite to SL, site which [10]. can After take the 4–6 young weeks become depending on theindependent growth rate and of disperse, fry that the varies pair frombond sitebetween to site the [ 10adults]. After dissolves the young and the become male may independent form a pair and disperse,bond thewith pair a new bond female between and the adults again, dissolves often reusing and the the same male lair may (Figure form 4). a Males pair bond may withspawn a new femaleup andto four spawn times again, within oftena 5-month reusing dry season the same whereas lair (Figure most females4). Males spawn may only spawn once. up to four times within a 5-month dry season whereas most females spawn only once. Because only the largest males monopolize spawning lairs and spawn repeatedly in them, the operational sex ratio is skewed, and females compete intrasexually for access to males that possess a lair leading to sexual dichromatism [11]. When not guarding young, males have a dull-colored olive-grey background, often with a dull yellow hue, and dark gray barring. The black and white barring pattern becomes highly contrasting (like the uniforms of prison convicts) when guarding young. Females have three color phases. Similar to males, females are cryptic olive-gray (never with yellow hue) with grey

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100 2.0 Males Females Males Females 90 Diversity 2020, 12, 136 4 of 15 80 1.5 70 barring when not reproductive, while parental females become highly aposematic with conspicuous 60 bright black and white barring (Figure5). Gravid females become blackened lending high contrast for gold flecks50 on the region of their abdomen that swells1.0 when gravid with eggs (presumably serving 40 as eggPercentage mimics?), yellow pigments in the webbing of the dorsal fin and blue pigment in the gular region30 [11]. In addition to these color changes, black-phase females actively court parental males that

Number of lairs used of lairs Number 0.5 are paired20 with other females [12] and fight intrasexually for access to males that possess a spawning lair (see video in supplementary materials). Pairs may form before selecting a spawning lair, but often Diversity10 2020, 12, x FOR PEER REVIEW 4 of 15 the male already possesses a lair from a previous bout of reproduction. 0 0.0 1234 234 100 2.0 Males Females Males Females 90 Seasonal mating frequency Seasonal mating frequency

80 (a) (b) 1.5 70 Figure 4. (a) Seasonal mating frequency (Dec–May) for males and females for all sites combined. 28% 60of males spawned more than once, 5% of females spawned more than once. (b) Mean ± SE number of spawning lairs used as a function of seasonal mating frequency. Males often reused the same site for 50 1.0 sequential broods. Data from [11]. 40 Percentage 30Because only the largest males monopolize spawning lairs and spawn repeatedly in them, the

Number of lairs used of lairs Number 0.5 operational20 sex ratio is skewed, and females compete intrasexually for access to males that possess a lair leading to sexual dichromatism [11]. When not guarding young, males have a dull-colored olive- grey10 background, often with a dull yellow hue, and dark gray barring. The black and white barring pattern0 becomes highly contrasting (like the uniforms0.0 of prison convicts) when guarding young. Females have1234 three color phases. Similar to males, females are cryptic234 olive-gray (never with yellow hue) with greySeasonal barring mating when frequencynot reproductive, while parental femalesSeasonal become mating frequencyhighly aposematic with conspicuous bright black and white barrin g (Figure 5). Gravid females become blackened lending high contrast(a) for gold flecks on the region of their abdomen that swells(b) when gravid with eggs (presumably serving as egg mimics?), yellow pigments in the webbing of the and blue pigmentFigureFigure 4. in(a the)4. Seasonal (a gular) Seasonal region mating mating [11]. frequency frequency In addition (Dec–May) (Dec–May) to these for males malescolor andchanges, and females females black-phase for for all allsites sites combined. females combined. actively28% 28% of males spawned more than once, 5% of females spawned more than once. (b) Mean ± SE number of courtof males parental spawned males more that thanare paired once, 5%with of other females females spawned [12] and more fight than intrasexually once. (b) Mean for accessSE number to males of spawning lairs used as a function of seasonal mating frequency. Males often reused the same± site for thatspawning possess lairs a spawning used as alair function (see video of seasonal in supplem matingentary frequency. materials). Males Pairs often may reused form before the same selecting site for sequential broods. Data from [11]. asequential spawning broods.lair, but Data often from the male [11]. already possesses a lair from a previous bout of reproduction. Because only the largest males monopolize spawning lairs and spawn repeatedly in them, the operational sex ratio is skewed, and females compete intrasexually for access to males that possess a lair leading to sexual dichromatism [11]. When not guarding young, males have a dull-colored olive- grey background, often with a dull yellow hue, and dark gray barring. The black and white barring pattern becomes highly contrasting (like the uniforms of prison convicts) when guarding young. Females have three color phases. Similar to males, females are cryptic olive-gray (never with yellow hue) with grey barring when not reproductive, while parental females become highly aposematic with conspicuous bright black and white barring (Figure 5). Gravid females become blackened lending high contrast for gold flecks on the region of their abdomen that swells when gravid with eggs (presumably serving as egg mimics?), yellow pigments in the webbing of the dorsal fin and blue pigment in the gular region [11]. In addition to these color changes, black-phase females actively court parental males that are paired with other females [12] and fight intrasexually for access to males that possess a spawning(a) lair (see video in supplem(b) entary materials). Pairs may form(c) before selecting a spawning lair, but often the male already possesses a lair from a previous bout of reproduction. Figure 5. Color phases of convict cichlids. Males alternate between drab olive-gray when non

reproductive as in the upper fish in (a), to contrasting black and white when defending young (female is ahead of the male in this image) (b). Females have an additional color phase when gravid and courting males in which the background color become black as in the lower fish in (a), image (c), which provides a striking contrast for gold flecks on the belly and yellow and blue pigments in the fins and throat. Photos of fish in hand by Brian Wisenden, photo of breeding pair (b) by Terence Lee.

Eggs are glued to the ceiling of the lair by the female and fertilized by the male. Females do most of the direct care of the embryos while they remain glued to the ceiling of the lair and, in a few days, after

(a) (b) (c)

Diversity 2020, 12, 136 5 of 15 they hatch into “free embryos” (eleuthroembryos or “wrigglers”) that form a trembling heap on the floor of the lair. During this time the male patrols the vicinity outside the lair to repel intruders. After a few more days, the wrigglers absorb their yolk and develop their fins and become free-swimming. In Costa Rican streams they emerge from the lair at a size of 4.5–5.0 SL and begin exogenous feeding on the substrate, all the while guarded by both parents. There is genetic [13] and morphological [14] evidence that convict cichlids are socially monogamous but not necessarily genetically monogamous. How the genetic structure of families may affect parental care has not been explored.

4. Parental Brood Defense In Costa Rican streams, free-swimming young (“fry”) form a two-dimensional disc on the substrate. Rarely do individual fry rise up into the water column, presumably because river current above the boundary layer would sweep them away, and because interstitial spaces in the substrate are their refuge from brood predators. Parents are positioned centrally, hovering a few centimeters above the substrate and facing in opposite directions from each other, to provide 360◦ vigilance for the approach of intruders. Not all intruders pose the same degree of threat to the offspring. Poeciliids, especially Poecilia gillii, are common intruders but do not attack cichlid fry. The schooling characin Astyanax fasciatus also pass over broods and are merely nudged away by the parents. Astyanax attack offspring only if the brood is first disturbed by another cause, such as human manipulations of the brood, or an attack by large adult dovii. Once an Astyanax attack begins, 50 or more others join in and overwhelm the defenses of the parents, which can disperse fry from the brood area, where they either find their way home using visual and chemical cues [12,15] or join neighboring families [16]. Parental defense attacks are most frequently directed against juvenile cichlids. In the Río Cabuyo and Quebrada Amores system, there were three species of cichlids: convict cichlids, a sand-sifting species Cribroheros longimanus, and the piscivorous P. dovii. Juvenile P. dovii were attacked from the greatest distances from the brood, suggesting that parents consider them as the most serious threat to their young (Figure6). Indeed, juvenile P. dovii were often observed sneaking up on broods by creeping stealthilyDiversity forward 2020, 12 under, x FOR thePEER cover REVIEW of leaf litter and hiding behind pebbles to stage an ambush.6 of 15 180 AST POEC 160 Juv CC Ad CC 140 Long Dovii 120

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0 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 Attack Radius (cm)

Figure 6.FigureParental 6. Parental brood brood defense defense attacks attacks per 10 10 min min observation observation period period (n = 840 (n trials)= 840 against trials) the against the characincharacinAstyanax Astyanax fasciatus fasciatus(AST), (AST), PoeciliaPoecilia gillii gillii (POEC),(POEC), juvenile juvenile convic convictt cichlids cichlids (Juv CC), (Juv adult CC), adult convict cichlidsconvict cichlids (Ad CC), (Ad CC), sand-sifter sand-sifter cichlid cichlidCribroheros Cribroheros longimanuslongimanus (Long),(Long), or juveniles or juveniles of the of piscivore the piscivore Parachromis dovii (Dovii). Line represents overall frequency distribution of parental attacks against Parachromis dovii (Dovii). Line represents overall frequency distribution of parental attacks against brood predators. Data from [10,17]. brood predators. Data from [10,17].

100 100

75 80

60 50

40

Number of Young Number of 27 25 20 Percent of Broods Surviving Percent of Broods

0 0 Lair < 6 6 - 8 8 - 10 > 10 < 6 6 - 8 8 - 10 > 10 Standard length of young (mm) Standard length of young (mm)

(a) (b)

Figure 7. (a) Percentage of broods surviving at various intervals between emergence from the lair until independence from parental care after the young reach 10 mm SL. (b) Number of young in broods at these same intervals for each site. Although there were site differences in brood size initially, all site-years converged on an average of 27 fry at independence. Solid symbols, pool habitat; open symbols, stream habitat. Circles, Río Cabuyo; triangles, Quebrada Amores. Solid lines, 1990; dashed lines, 1991. Data from [9].

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180 AST POEC 160 Juv CC Ad CC 140 Long Dovii 120

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80 Frequency

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20 In spite of parental vigilance and brood defense, predators take their toll and reduce the number of young in a brood,0 and ultimately, the number of broods that persist with surviving offspring to fry independence. Brood0 success 5 10 15 (at least20 25 one 30 fry 35 surviving 40 45 50 to 55 independence) 60 65 70 75 is 80 strongly 85 90 linked to habitat Attack Radius (cm) (Figure7a). In shallow sections of the streams (i.e., “stream” sites), brood survival was relatively high (48%) comparedFigure 6. Parental to broods brood reared defense in theattacks deeper per 10 “pool” min observation sections of period the river (n = (15%).840 trials) Contributing against the factors to thischaracin disparity Astyanax may be fasciatus that P. (AST), dovii spawnPoecilia ingillii the (POEC), deepsections juvenile ofconvic thet rivers,cichlids thus (Juv theirCC), juvenilesadult are more abundantconvict cichlids there (Ad than CC), in sand-sifter the shallow cichlid sections Cribroheros of thelongimanus streams, (Long), and or because juveniles deeper of the piscivore sections of the river areParachromis darker anddovii parental (Dovii). Line detection represents of approaching overall frequency brood distribution predators of mayparental be impairedattacks against under these conditions.brood predators. For those Data broods from that[10,17]. had young survive to independence, the final number of young averaged 27 despite widely ranging starting numbers, parent size and habitat (Figure7b).

100 100

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Number of Young Number of 27 25 20 Percent of Broods Surviving Percent of Broods

0 0 Lair < 6 6 - 8 8 - 10 > 10 < 6 6 - 8 8 - 10 > 10 Standard length of young (mm) Standard length of young (mm)

(a) (b)

FigureFigure 7. 7.( a()a Percentage) Percentage of of broods broods surviving surviving at at various various intervals intervals between between emergence emergence from from the the lair lair until independenceuntil independence from parentalfrom parental care aftercare theafter young the young reach reach 10 mm 10 SL.mm ( bSL.) Number (b) Number of young of young in broods in atbroods these sameat these intervals same intervals for each for site. each Althoughsite. Although there there were were site site di ffdifferenceerences ins in brood broodsize size initially, all site-yearsall site-years converged converged on on an an average average of of 27 27 fry fry at at independence. independence. Solid Solid symbols, symbols, pool pool habitat; habitat; open open symbols,symbols, stream stream habitat. habitat. Circles,Circles, Río Río Cabuyo; tr triangles,iangles, Quebrada Quebrada Amores Amores.. Solid Solid lines, lines, 1990; 1990; dashed dashed lines,lines, 1991. 1991. Data Data from from [[99].].

The convergence of offspring number of successful broods to 27 young suggested that there may be constraints on maximum brood size imposed by the logistics of brood defense (Lack’s Hypothesis). This was confirmed by a field manipulation experiment (Figure8a). This experiment also demonstrated that per capita growth rate of the young was inversely proportional to the number of young in the brood, suggesting that the logistic constraint was the area defined by the effective radius of parental brood defense (Figure8b). In large broods, young were forced to crowd into the safe area defendable by the parents and therefore foraged less than young in small broods. Diversity 2020, 12, x FOR PEER REVIEW 7 of 15

The convergence of offspring number of successful broods to 27 young suggested that there may be constraints on maximum brood size imposed by the logistics of brood defense (Lack’s Hypothesis). This was confirmed by a field manipulation experiment (Figure 8a). This experiment also demonstrated that per capita growth rate of the young was inversely proportional to the number of young in the brood, suggesting that the logistic constraint was the area defined by the effective radius of parental brood defense (Figure 8b). In large broods, young were forced to crowd into the safe area Diversitydefendable2020, 12 by, 136 the parents and therefore foraged less than young in small broods. 7 of 15

160 0.3 *** Augmented * 140 Control 0.25 NS 120 0.2 100 NS 18 0.15 80 13 9 60 0.1 8 40 Number of young Number 0.05 20 Growth rate (mm/day) 0 0 Pre-manip Day 0 Day 20 Augmented Control

(a) (b)

FigureFigure 8. 8.( (aa)) Lack’sLack’s hypothesishypothesis isis thatthat maximum brood size size is is limited limited by by the the number number of of offspring offspring that that cancan be be reared reared to independence,to independence, not bynot the by physiological the physiological capacity capacity to produce to produce eggs. Naturally-occurring eggs. Naturally- broodsoccurring in the broods Río Cabuyo in the Río were Cabuyo either were left unmanipulatedeither left unmanipulated (control) or (c augmentedontrol) or augmented with extra with fry to extra have 150fry young.to have Experimental 150 young. Experimental broods were unablebroods to were sustain unable numerical to sustain advantage numerical of the advantage manipulation of the by themanipulation end of 20 days. by the (b end) Individual of 20 days. growth (b) Individual rates of larvae growth in experimentalrates of larvae broods in experimental were significantly broods lowerwere thansignificantly larvae in controllower than broods larvae due toin crowdingcontrol broods within due the parentally-defendedto crowding within area the and parentally- therefore experienceddefended area increased and therefore competition experien forced food. increased * p < 0.05, competition *** p < 0.001. for food. Data * fromp < 0.05, [18 ].*** p < 0.001. Data from [18]. 5. Broods of Mixed Parentage and Intraspecific Brood Adoption 5. BroodsRecent of genetic Mixed analysesParentage of and convict Intraspecific cichlid broodsBrood Adoption in Río Cabuyo show evidence of multiple maternity,Recent multiple genetic paternity, analyses andof convict wholesale cichlid adoption brood ofs in young Río Cabuyo unrelated show to either evidence parent of providingmultiple carematernity, [13]. An multiple alternative paternity, “sneaker” and male wholesale morph adopti has beenon of observed young unrelated in Laguna to de either Xiloá parentin Nicaragua providing [14 ]. Clearly,care [13]. the An mating alternative system “sneaker” of this male species morph is one has of been social observed monogamy in Laguna but not de geneticXiloá in monogamy.Nicaragua In[14]. addition Clearly, to the multiple mating system parentage, of this convict species cichlids is one of also social add monogamy offspring but to not their genetic brood monogamy. during the free-swimmingIn addition to multiple stage while parentage, the young convict are cichlids being guarded also add [ 19offspring]. In tracking to their the brood number during of youngthe free- in individualswimming broods stage overwhile time, the ityoung was often are observedbeing guarde thatd the [19]. number In tracking of young the in somenumber broods of young increased in insteadindividual of decreasing broods over over ti time.me, it In was these often cases, observed and in others that the in whichnumber the of number young of in young some declined,broods thereincreased appeared instead within of decreasing the brood over two distincttime. In sizethese classes: cases, and one in that others tracked in which the growth the number trajectory of young of the youngdeclined, “related” there toappeared the adults within providing the brood care, andtwo additional distinct size young classes: that wereone that smaller tracked than the younggrowth of thetrajectory host family of the (Figure young9 “related”). Adoption to the was adults not a providing case of misdirected care, and parentaladditional care young because that experimentalwere smaller additionthan the ofyoung young of thatthe host were family similar (Figure in size 9). orAdop smallertion was than not host a case young of misdirected were always parental successfully care adopted,because experimental whereas young addition larger of than young host that young were were similar always in size rejected or smaller [19]. than Close host examination young were of naturalalways adoption successfully events adopted, revealed whereas that size young discrimination larger than occurredhost young only were until always host young rejected were [19]. between Close 7examination and 8 mm SL, of andnatural thereafter adoption there events was norevealed size bias that (Figure size discrimination9). occurred only until host youngWe were hypothesized between 7 and that 8 size-biasmm SL, and in therea broodfter adoption there was was no drivensize bias by (Figure differential 9). swimming performance between small and large young. Predation trials in the lab on broods of mixed sized demonstrated that predators preferentially consumed small fry (Figure9) and a brood manipulation experiment in the field confirmed that parents that adopt additional young benefit from increasing the survival rate of their “own” young through statistical dilution of predation risk, and through differential predation on smaller adopted young [20].

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6 P. dovii 12.5 A. siquia 11.5 5

10.5 4 9.5

8.5 3 7.5 2 6.5 eaten Number

5.5 1 4.5 Standard length of adopted young adopted of Standard length 3.5 0 57911 5678 SL of young (mm) Standard length of host family's young

(a) (b)

FigureFigure 9. (a )9. Size-biased (a) Size-biased conspecific conspecific adoption adoption of broodsof broods from from neighboring neighboring families. families. Line Line is is y y= =x. x. When youngWhen are adoptedyoung are from adopted neighboring from neighboring families, families, parents parents accept accept young young that that are are smaller smaller than than their their own and rejectown and those reject that those are largerthat are than larger their than own their (data own (data not shown), not shown), until until the the host host young young are are larger larger than than 8 mm SL. This raised the possibility that adopted young are being set up as targets for predators 8 mm SL. This raised the possibility that adopted young are being set up as targets for predators to to spare predation on host young, which was confirmed in a subsequent field experiment. (b) Hunting spare predation on host young, which was confirmed in a subsequent field experiment. (b) Hunting success of juvenile convict cichlids and juvenile P. dovii on groups of convict cichlid fry of mixed sizes. success of juvenile convict cichlids and juvenile P. dovii on groups of convict cichlid fry of mixed sizes. Small fry were eaten significantly more often than large fry. Data from [18]. Small fry were eaten significantly more often than large fry. Data from [18]. We hypothesized that size-bias in brood adoption was driven by differential swimming 6. Ontogeny of Antipredator Competence performance between small and large young. Predation trials in the lab on broods of mixed sized Burstdemonstrated speed of that young predators at diff erentpreferentially lengths consumed showed that small young fry (Figure became 9) fasterand a brood swimmers manipulation as they grew and developed,experiment butin the that field the confirmed rate of increase that parents was notthat linearadopt additional (Figure 10 young). Post-hoc benefit pairwise from increasing comparison tests showedthe survival that rate swimming of their “own” performance young through rapidly improvedstatistical dilution after the of youngpredation reached risk, and 7 mm through SL, which differential predation on smaller adopted young [20]. coincides with the size at which parents no longer discriminate on the basis of size when they adopt Diversity 2020, 12, x FOR PEER REVIEW 9 of 15 new young6. Ontogeny into their of Antipredator families. Competence

0.45Burst speed of young at different lengths showed that3.5 young became faster swimmers as they

grew and developed,RC LX but that the rate of increase was) not linearRC (FigureLX 10). Post-hoc pairwise 0.40 c c -2 comparison tests showed that swimming performance rapidly3.0 improved after the young reachedc 7 ) mm-1 0.35SL, which coincides with the size at which parents no longer discriminate on thec basis of size 2.5 when0.30 they adopt new young into their families.n b 2.0 0.25 b n m 0.20 a a m 1.5 m a a m 0.15 m m m 1.0 m 0.10 0.5 0.05 Maximum velocity (ms Maximum Maximum acceleration (ms 0.00 0.0 56789 56789 Fry SL (mm) Fry SL (mm) (a) (b)

1 −1 −2 FigureFigure 10. ( 10.a) Maximum(a) Maximum velocity velocity (m (m·ss− ) and) and (b ()b acceleration) acceleration (m (m·ss− )) for for cichlid cichlid fry fry of of lengths lengths 5 5to to 9 9 mm mm SL, from parents from Río ·Cabuyo (RC) in Costa Rica and· from Laguna de Xiloá (LX) in SL, from parents from Río Cabuyo (RC) in Costa Rica and from Laguna de Xiloá (LX) in Nicaragua. LettersNicaragua. above bars Letters indicate above post-hocbars indicate pairwise post-hoc comparison pairwise comparison tests across tests fry across sizes fry within sizes within each site.each Data fromsite. [17 ,Data21]. from [17,21].

7. Timing of Ossification of the Larval Skeleton from Cartilage to Bone The skeleton of larval fish is cartilaginous at the time of hatching and then becomes ossified into bone in the transition from larvae to juvenile. Bone is stronger than cartilage and leads to more forceful swimming propulsion. Larvae that had been cleared and stained with alcian blue (cartilage) and alizarin red (bone) allowed us to quantify the timing of the transition from cartilage to bone (Figure 11). Ordination of the resulting data matrix revealed that rapid calcification of the skeleton occurred at around 7 mm SL, which coincides with changes in swimming performance, differential predation and discriminatory brood adoption on the basis of size (Figure 12). Taken together, these data show that predation on larval convict cichlids exerts selection pressure on the timing of developmental events, which affect the growth and survival rates of the young, and shapes the evolution of parental brood defense.

(a) (b)

Figure 11. (a) Cleared and stained larvae and juveniles with alcian blue (cartilage) and alizarin red (bone) for Río Cabuyo fish sized 5–9 mm SL. (b) Each specimen was imaged at high magnification so

Diversity 2020, 12, x FOR PEER REVIEW 9 of 15

0.45 3.5

RC LX ) RC LX

0.40 c c -2 3.0 c )

-1 0.35 c 2.5 0.30 n b 2.0 0.25 b n m 0.20 a a m 1.5 m a a m 0.15 m m m 1.0 m 0.10 0.5 0.05 Maximum velocity (ms Maximum Maximum acceleration (ms 0.00 0.0 56789 56789 Fry SL (mm) Fry SL (mm) (a) (b)

Figure 10. (a) Maximum velocity (m·s−1) and (b) acceleration (m·s−2) for cichlid fry of lengths 5 to 9 mm SL, from parents from Río Cabuyo (RC) in Costa Rica and from Laguna de Xiloá (LX) in DiversityNicaragua.2020, 12 Letters, 136 above bars indicate post-hoc pairwise comparison tests across fry sizes within each 9 of 15 site. Data from [17,21].

7. 7.Timing Timing of ofOssification Ossification of of the the Larv Larvalal Skeleton Skeleton from from Ca Cartilagertilage to to Bone Bone TheThe skeleton skeleton of oflarval larval fish fish is iscartilaginous cartilaginous at atth thee time time of ofhatching hatching and and then then becomes becomes ossified ossified into into bonebone in in the the transition transition from larvaelarvae toto juvenile. juvenile. Bone Bone is strongeris stronger than than cartilage cartilage and leadsand leads to more to forcefulmore forcefulswimming swimming propulsion. propulsion. Larvae Larvae that hadthat beenhad been cleared cleared and and stained stained with with alcian alcian blue blue (cartilage) (cartilage) and andalizarin alizarin red red (bone) (bone) allowed allowed us to us quantify to quantify the timing the timing of the transitionof the transition from cartilage from cartilage to bone (Figureto bone 11 ). (FigureOrdination 11). Ordination of the resulting of the dataresulting matrix data revealed matrixthat revealed rapid that calcification rapid calcification of the skeleton of the occurred skeleton at occurredaround at 7 mmaround SL, 7 which mm SL, coincides which coincides with changes with inchanges swimming in swimming performance, performance, differential differential predation predationand discriminatory and discriminatory brood adoption brood adoption on the basis on the of sizebasis (Figure of size 12 (Figure). Taken 12). together, Taken together, these data these show datathat show predation that predation on larval convicton larval cichlids convict exerts cichli selectionds exerts pressure selection on pressure the timing on of the developmental timing of developmentalevents, which events, affect the which growth affect and the survival growth rates an ofd survival the young, rates and of shapes the young, the evolution and shapes of parental the evolutionbrood defense. of parental brood defense.

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FigureFigure 11. 11. (a)( aCleared) Cleared and and stained stained larvae larvae and and juveniles juveniles with with alcian alcian blue blue (cartilage) (cartilage) and and alizarin alizarin red red that each of 111 skeletal elements could be scored for degree of ossification on a scale of 1–4. Photos (bone)(bone) for for Río R íCabuyoo Cabuyo fish fish sized sized 5–9 5–9 mm mm SL. SL. (b) ( bEach) Each specimen specimen was was imaged imaged at athigh high magnification magnification so so by Tony Stumbo. Data from [17]. that each of 111 skeletal elements could be scored for degree of ossification on a scale of 1–4. Photos by Tony Stumbo. Data from [17].

0.3 0.3 6 mm Stress = 0.07 6 mm Stress = 0.03 7 mm 7 mm 8 mm 8 mm 9 mm 9 mm

0 0 NMDS 2 NMDS NMDS 2 NMDS

-0.3 -0.3 -0.6NMDS 0 1 0.6 -0.6NMDS 0 1 0.6

(a) (b)

FigureFigure 12.12.( a(a)) Non-metric Non-metric dimensional dimensional scaling scaling (NMDS) (NMDS) axes axes for 111 for bones 111 bones125 larvae× 125 fromlarvae Rí ofrom Cabuyo. Río × ThereCabuyo. was There no variation was no in variation 5 mm fry in (not 5 mm shown). fry (not Pairwise shown). comparisons Pairwise revealedcomparisons that ossificationrevealed that of 6ossification mm fry < 7of= 68 mm= 9 mmfry < SL 7 = fry. 8 = (9b )mm NMDS SL fry. ordination (b) NMDS of images ordination from of larvae images from from lab-F1 larvae adults from from lab- LagunaF1 adults de from Xiloá .Laguna Again 5de mm Xiloá. SL fish Again contained 5 mm noSL variationfish contained (not shown), no variat bution the (not conspicuous shown), but shift the in ossificationconspicuous was shift between in ossification 8 mm fry was and between 9 mm fry.8 mm Data fry from and [917 mm,21]. fry. Data from [17,21].

8. Comparison to Convict Cichlids in Laguna de Xiloá, Nicaragua Data from Costa Rican streams indicate a correlation among predation pressure, larval development and parental care. Laguna de Xiloá is a volcanic crater lake in Nicaragua that differs from Costa Rican streams in several ways. It is lentic, it is not shaded by riparian vegetation therefore there is rich autochthonous production, and there is a diverse fish community including the sleeper goby Gobiomorus dormitor, which is a specialist predator on the larvae of cichlids. We collected and preserved larvae from convict cichlid broods from Laguna de Xiloá for analysis of ossification. Ordination of those data revealed that the timing of ossification was different than for fishes in the Rió Cabuyo system, being delayed to between 8 and 9 mm SL (Figure 12). Adults collected from Laguna de Xiloá and bred in the same laboratory tanks used to produce data for the Costa Rican population (i.e., common garden), showed that larvae from Nicaraguan parents showed delayed onset of swimming performance relative to Costa Rican fish. Maximum velocity and acceleration did not noticeably improve until the young were larger than 8 mm SL (Figure 10), which matches well with data on skeletal ossification, and presumably would continue to improve beyond 9 mm SL.

9. Correlation of Parental Brood Defense and Brood Predators Growth rates of larvae showed that there is a limit to the area that can be effectively defended by two adults. Interacting with this constraint is the swimming speed of the young that enable them to evade an attack by a brood predator. When the young are small and weak-swimming, they occupy a small area that can be effectively guarded. As the young develop and improve in swimming performance, the area occupied by the brood should be expected to expand to reduce intrabrood competition for food. Measurements of brood diameter in the Rió Cabuyo and Laguna de Xiloá confirm that brood area does indeed expand as the young grow and develop into faster swimmers [21]. Change point analysis of brood radius indicates that in the Rió Cabuyo brood radius expands until the young are about 6.45 mm SL, and then levels off, whereas in Laguna de Xiloá brood area remains tight and cohesive until the young reach 7.9 mm SL and then expands in radius thereafter (Figure 13). In both cases, the switch points coincide with site-specific switch points in swimming performance and skeletal ossification. The reason(s) for why brood radius increases then plateaus in

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8. Comparison to Convict Cichlids in Laguna de Xiloá, Nicaragua Data from Costa Rican streams indicate a correlation among predation pressure, larval development and parental care. Laguna de Xiloá is a volcanic crater lake in Nicaragua that differs from Costa Rican streams in several ways. It is lentic, it is not shaded by riparian vegetation therefore there is rich autochthonous production, and there is a diverse fish community including the sleeper goby Gobiomorus dormitor, which is a specialist predator on the larvae of cichlids. We collected and preserved larvae from convict cichlid broods from Laguna de Xiloá for analysis of ossification. Ordination of those data revealed that the timing of ossification was different than for fishes in the Rió Cabuyo system, being delayed to between 8 and 9 mm SL (Figure 12). Adults collected from Laguna de Xiloá and bred in the same laboratory tanks used to produce data for the Costa Rican population (i.e., common garden), showed that larvae from Nicaraguan parents showed delayed onset of swimming performance relative to Costa Rican fish. Maximum velocity and acceleration did not noticeably improve until the young were larger than 8 mm SL (Figure 10), which matches well with data on skeletal ossification, and presumably would continue to improve beyond 9 mm SL.

9. Correlation of Parental Brood Defense and Brood Predators Growth rates of larvae showed that there is a limit to the area that can be effectively defended by two adults. Interacting with this constraint is the swimming speed of the young that enable them to evade an attack by a brood predator. When the young are small and weak-swimming, they occupy a small area that can be effectively guarded. As the young develop and improve in swimming performance, the area occupied by the brood should be expected to expand to reduce intrabrood competition for food. Measurements of brood diameter in the Rió Cabuyo and Laguna de Xiloá confirm that brood area does indeed expand as the young grow and develop into faster swimmers [21]. Change point analysis of brood radius indicates that in the Rió Cabuyo brood radius expands until the young are about 6.45 mm SL, and then levels off, whereas in Laguna de Xiloá brood area remains tight and cohesive until the young reach 7.9 mm SL and then expands in radius thereafter (Figure 13). In both cases, the switch points coincide with site-specific switch points in swimming performance and skeletal ossification. The reason(s) for why brood radius increases then plateaus in Rió Cabuyo but remains small and only later expands in Laguna de Xiloá is not known, but is likely due to a combination of relative predator pressure and relative productivity. Food is richly abundant in Laguna de Xiloá and so too is predator density and effectiveness. The best strategy for larvae (and their parents) in Laguna de Xiloá may be to stay huddled in a tight group for minimum risk to brood predators. They can afford to use this strategy because algal mats and associated epiphytic fauna are abundant in the shallow waters of Laguna de Xiloá where our data were collected. In contrast, the Rió Cabuyo is a low-order stream shaded almost completely by riparian canopy even in the dry season, thus food availability is less abundant. That, in combination with a relatively benign predator community, may favor early expansion of brood radius and therefore early ossification of the skeleton. Diversity 2020, 12, x FOR PEER REVIEW 11 of 15

Rió Cabuyo but remains small and only later expands in Laguna de Xiloá is not known, but is likely due to a combination of relative predator pressure and relative productivity. Food is richly abundant in Laguna de Xiloá and so too is predator density and effectiveness. The best strategy for larvae (and their parents) in Laguna de Xiloá may be to stay huddled in a tight group for minimum risk to brood predators. They can afford to use this strategy because algal mats and associated epiphytic fauna are abundant in the shallow waters of Laguna de Xiloá where our data were collected. In contrast, the Rió Cabuyo is a low-order stream shaded almost completely by riparian canopy even in the dry season, thus food availability is less abundant. That, in combination with a relatively benign predator community, may favor early expansion of brood radius and therefore early ossification of the skeleton.Diversity 2020 , 12, 136 11 of 15

30

20 Brood radius (cm) 10

RC <= 6.45 LX <= 7.9

RC > 6.45 LX > 7.9

0 4 6 8 10 12 14 16 18 Fry SL (mm)

FigureFigure 13. 13. TheThe radius radius of of broods broods being being guarded guarded in in Río Río Cabu Cabuyoyo (circles) (circles) and and Laguna Laguna de de Xiloá Xiloá (triangles)(triangles) fromfrom time time of of early early emergence emergence from from the the spawning spawning lair lair to to the the point point of of independence independence from from parental parental care. care. Change-pointChange-point analysis analysis revealed revealed non nonlinearitylinearity occurred occurred at at SL SL = 6.45= 6.45 in inRío R Cabuyoío Cabuyo fish fish and and SL SL= 7.9= for7.9 fishfor fishin Laguna in Laguna de deXiloá. Xilo Theseá. These switch switch points points coin coincidecide with with changes changes in in skeletal skeletal ossification ossification or or the the young, ontogenetic shifts in swimming swimming performance performance and changes in parental parental adoption adoption behavior. Data Data fromfrom [21]. [21]. 10. Discussion 10. Discussion Brood defense is, in part, a matter of geometry (Figure 14). Risk of predation increases with Brood defense is, in part, a matter of geometry (Figure 14). Risk of predation increases with distance from the brood center where the parents are positioned. The zone circumscribed by a radius distance from the brood center where the parents are positioned. The zone circumscribed by a radius of two body lengths is a zone of intimidation (zone A in Figure 14). Few attacks occur within this of two body lengths is a zone of intimidation (zone A in Figure 14). Few attacks occur within this central area because intruders almost never approach the brood center. Aposematic coloration adopted central area because intruders almost never approach the brood center. Aposematic coloration by convict cichlids during the parental phase presumably help the young track the position of their adopted by convict cichlids during the parental phase presumably help the young track the position parents, but they also warn intruders of the presence of highly aggressive fish. of their parents, but they also warn intruders of the presence of highly aggressive fish. Beyond a radius of 10 cm, parental attack rates quickly escalate, peaking for attack radii from 25 Beyond a radius of 10 cm, parental attack rates quickly escalate, peaking for attack radii from 25 and 45 cm (zone C in Figure 14). Attacks with radii larger than 25 cm are usually a quick burst out to and 45 cm (zone C in Figure 14). Attacks with radii larger than 25 cm are usually a quick burst out to intercept the intruder followed by a quick return to the brood center because driving a predator away intercept the intruder followed by a quick return to the brood center because driving a predator away requires that the parent must temporarily leave their brood vulnerable to attack from the opposite requires that the parent must temporarily leave their brood vulnerable to attack from the opposite direction. Parents differentially attack species that pose a greater threat to the young, namely juvenile direction. Parents differentially attack species that pose a greater threat to the young, namely juvenile conspecifics and juvenile P. dovii. Juvenile convict cichlids are opportunistic predators, numerically conspecifics and juvenile P. dovii. Juvenile convict cichlids are opportunistic predators, numerically abundant in this system and attacked frequently. P. dovii are piscivores and although not common in abundant in this system and attacked frequently. P. dovii are piscivores and although not common in this system, judging by attack distances, P. dovii represent a greater threat to cichlid fry than conspecific juveniles do. Zones of parental protection constrain how far fry can stray from their parents while foraging. There is a trade-off for young between foraging (growth) and risk of predation. This trade-off shifts as swimming performance improves. Brood diameter increased with fry SL independent of the number of young in the brood [17]. Note that brood radii for convict cichlid broods in the Río Cabuyo do not extend beyond 20 cm until after the skeleton has fully ossified. In Laguna de Xiloá the relationship between development of the young and brood radius is the inverse of the pattern observed in the Río Cabuyo. Young in both populations remain in a tight shoal until they attain a length that coincides with skeletal ossification and then begin to stray from their parents. Larval and juvenile convict Diversity 2020, 12, 136 12 of 15

Diversity 2020, 12, x FOR PEER REVIEW 12 of 15 cichlids in Laguna de Xiloá remain with their parents until they have grown much larger than typical size-at-dispersalthis system, judging observed by forattack broods distances, in Río Cabuyo. P. dovii This represent may reflect a greater greater threat threat ofto predationcichlid fry and than/or richerconspecific food, orjuveniles other unmeasured do. parameters in the laguna.

Predators

10 25 45 cm

A B C D

FigureFigure 14.14. GeometryGeometry ofof broodbrood defensedefense inin convictconvict cichlidscichlids inin RRíoío CabuyoCabuyo thatthat incorporatesincorporates datadata onon parentalparental attackattack distances,distances, broodbrood radiusradius datadata andand thethe trade-otrade-offff for forfry fry between between maximizingmaximizing foragingforaging whilewhile minimizing minimizing risk risk of of predation.predation. A,A, zonezone ofof intimidationintimidation wherewhere physicalphysical presencepresence ofof parentsparents detersdeters approachapproach ofof broodbrood predators.predators. VeryVerysmall smallfry fryfrom fromR RíoíoCabuyo Cabuyostay stayhere here andand smallsmall andand medium-sizedmedium-sized fryfry from from Laguna Laguna de de Xilo Xiloáá stay stay here; here; B, transition B, transiti zoneon where zone frywhere can expandfry can into expand when into their when swimming their performanceswimming performance and predation and risk predation warrants risk it; warrants C, zone of it; interception C, zone of interception to maintain to a maintain predator-free a predator- buffer aroundfree buffer the brood;aroundD, the zone brood; of escalatedD, zone of attack, escalated particularly attack, particularly for juveniles for of juveniles the piscivore of theP. piscivore dovii. The P. evolutiondovii. The ofevolution parental of care parental in cichlids careis in a cichlids three-way is processa three-way between process brood between predators, brood ontogeny predators, of antipredatorontogeny of competenceantipredator in competence the fry, and in parental the fry, areaand defense.parental area defense.

TheZones direction of parental of change protection in ontogenetic constrain how timing far infry response can stray to from predation their parents could occurwhile inforaging. either direction.There is a Iftrade-off predation for selects young for between fast escape foraging responses (growt earlyh) and in development,risk of predation. then This one trade-off might predict shifts earlieras swimming onset of performance calcification. improves. A second possibilityBrood diamet is thater intenseincreased predation with fry risk SL selectsindependent for extended of the periodsnumber of of tight young shoaling in the brood behavior [17]. instead Note that of individual brood radii escape for convict responses, cichlid allowing broods in young the Río to allocateCabuyo moredo not resources extend intobeyond growth 20 incm physical until after size ratherthe skelet thanon to has ossification fully ossified. of skeletal In components.Laguna de Xiloá There the is supportrelationship for the between latter hypothesis development from populationof the young diff erencesand brood in pumpkinseed radius is the sunfish inverse (Lepomis of the gibbosus pattern), inobserved a population in the with Río fasterCabuyo. growth Young rates in showingboth populations delayed ossificationremain in a of tight cranial shoal bones until [22 they]. Similarly, attain a medakalength that (Oryzias coincides latipes with) from skeletal relatively ossification fast-growing and then populations begin to havestray fewer from skeletaltheir parents. supports Larval for finsand andjuvenile poorer convict swimming cichlids performance in Laguna that de Xiloá same-sized remain fish with from their slow-growing parents until populations they have [grown23]. It seems much likelylarger that than convict typical cichlids size-at-dispersal in Laguna de observed Xiloá have for been broods selected in Río for Cabuyo. fast growth This and may therefore reflect delayed greater skeletalthreat of ossification predation and/or until they richer have food, attained or other a relativelyunmeasured large parameters size compared in the tolaguna. convict cichlids in Río Cabuyo.The direction of change in ontogenetic timing in response to predation could occur in either direction. If predation selects for fast escape responses early in development, then one might predict 11. Conclusions earlier onset of calcification. A second possibility is that intense predation risk selects for extended periodsConvict of tight cichlids shoaling in Rio behavior Cabuyó inandstead Laguna of individual de Xiloá escapeare diff erentresponses, from oneallowing another. young Divergence to allocate in themore timing resources of skeletal into ossificationgrowth in physical leads to divergent size rather behavioral than to ossification phenotypes of of skeletal larvae. Wecomponents. know divergent There developmentis support for is the not latter a result hypothesis of developmental from popu plasticitylation differences or food availability in pumpkinseed because sunfish the ossification (Lepomis datagibbosus were), in derived a population from lab-reared with faster adults growth held rates under showing identical delayed conditions ossification (i.e., a of “common cranial bones garden”). [22]. PopulationSimilarly, medaka differences (Oryzias reflect geneticlatipes) difromfferences, relatively not environmental fast-growing ones.populations Skeletal have ossification fewer changesskeletal swimmingsupports for performance fins and andpoorer therefore swimming vulnerability performance to brood that predators, same-sized which fish in turnfrom altersslow-growing selection populations [23]. It seems likely that convict cichlids in Laguna de Xiloá have been selected for fast growth and therefore delayed skeletal ossification until they have attained a relatively large size compared to convict cichlids in Río Cabuyo.

Diversity 2020, 12, 136 13 of 15 on parental care behavior in terms of brood defense and fine-grain decision-making, such as when to accept or reject new young that join their brood. Allopatric population divergences are consistent with incipient speciation. Reproductively, isolation occurs by mechanisms of foraging competitive exclusion and reproductive behaviors including female mate choice, depth and timing of spawning, e.g., [24,25]. Laguna de Xiloá is well known for several examples of sympatric speciation of other cichlid species [26–28], a much younger evolutionarily radiation than the celebrated radiations that have occurred in cichlid species of the rift valley lakes in East Africa. Species radiations in cichlids in Laguna de Xiloá, and African rift valley cichlids radiated due to sexual selection or ecological niche partitioning. In contrast, it seems very likely that the cause of divergence in convict cichlid populations in Costa Rica streams and a Nicaraguan lake is predation. Predation is known to lead to population divergences in other systems (e.g., [29–32]). However, the interacting roles of larval development, larval antipredator competence, and parental care in driving species diversity is not well explored (but see [33,34]). These traits could be added to the list of traits that cause reproductive isolation through suppression of hybrid crosses. Brood defense is maintained by kin-selected benefits to parents derived from increased offspring survival. Across cichlids, patterns of parental care vary widely in terms of duration of care, whether care is uniparental, biparental or multigenerational, and whether eggs are attached to the substrate or incubated orally [35]. But in every case, predation on eggs, larvae and juveniles is the driver of selection for these behaviors and physiological mechanisms. Cichlids offer a remarkably diverse system with which to explore the relationship among predation, the evolution of parental care and species diversity. There are several potentially fruitful avenues for future study to explore the extent to which the phenomena described here apply to other populations and other species. The data presented here are based on two populations that differ in many ways, including predation pressure on fry. Inclusion of additional populations will increase resolution of the causal relationships between brood predators, food, temperature, spawning site availability, adult density, etc., that may all shape patterns of parental care. Non-cichlid species that provide care for their young offer an opportunity to test these relationships independent from phylogenetic effects. Ultimately, a goal of this research would be to develop a quantitative framework that integrates life history traits with the environmental factors that shape them.

Supplementary Materials: The following are available online at http://www.mdpi.com/1424-2818/12/4/136/s1, Video S1: Video of female-female intrasexual contest over a male. Funding: The data reported here were funded by the National Science and Research Council of Canada, and internal grants from Minnesota State University Moorhead from the Dille Fund for Excellence, and Faculty Research Grants to BDW. Acknowledgments: This review summarizes approximately 30 years of research on the evolutionary ecology of convict cichlids in the field and lab. I have had many collaborators in this effort, listed as coauthors in the cited references. Miles Keenleyside deserves special mention for expertly and patiently guiding the early stages of this work. Patricia (Bee) Wisenden was involved throughout the 30+ years of this research as a field assistant and life partner. Gordon and Jutta Frankie made the Costa Rican field work possible. Ken McKaye and Eric van den Berghe made work in Laguna de Xiloá possible, and Eric collected and shipped LX fish to my lab in Minnesota. Conflicts of Interest: The author declares no conflict of interest.

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