Luidia Foliolata Was Examined in the Laboratory

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This paper was submitted by the faculty of FAU’s Harbor Branch Oceanographic Institute.

Notice: ©1994 A. A. Balkema. This manuscript is an author version with the final publication available and may be cited as: George, S. B. (1994). Phenotypic plasticity in the larvae of Luidia foliata (Echinodermata: Asteroidea). In B. David, A. Guille, J. P. Feral, & M. Roux (Eds.), Echinoderms through Time: proceedings of the 8th International Echinoderm Conference, Dijon, France, 6-10 September 1993 (pp. 297-307). Rotterdam; Brookfield, VT: A.A. Balkema.

S.B.George Friday Harbor Laboratories, University ofWashington, Wash., USA

ABSTRACT: The effect offood ration on growth and development oflarvae ofthe seastar Luidia foliolata was examined in the laboratory. Different food rations led to different larval shapes. Larvae at the high food ration (10000 cells/ml) had arms with pointed ends and those at the low food ration (1000 cells/m]) had arms with rounded ends. Advanced bipinnaria at the low food ration were larger and had longer larval arms than those at the high food ration. Juveniles started appearing 85 days afterfertilization at the high food ration and 167 days afterfertilization for those at the low food ration. The diameters ofjuveniles produced did not differ significantly between food rations. The changes in shape associated with the low food ration should lead to greater clearance rates which would enhance growth rate of larvae, although still at a slower rate than for those at the high food ration. Developmental plasticity that allows changes in form in response to different food concentrations or food quality I11ay be a mechanism ofacclimation to different food supplies.

INTRODUCTION

Laboratory studies have shown that relatively When food is abundant growth is allocated to high concentrations of food organisms are re development of the rudiment and other cells quired for maximum rate of development of that are carried through metamorphosis rather echinoderm larvae (Fenaux et al. 1985, 1988). than into growth of larval arms. Olson et al. Although Olson (1987), Olson etat. (1987) and (1987) noted that plankton feeding asteroid Olson and Olson (1989) indicate that food larvae showed no tnorphological changes in limitation might not be a major factor in the environments with low phytoplankton con ecology of invertebrate larvae, some echi no centrations. Whether this is general among derm larvae seem to have developed mecha asteroid larvae is not known. The purpose of nisms to combat starvation.When food is scarce the present study was to ascertain how varying echinoid larvae increase arm length (Boidron food ration influenced: a) morphological Metairon 1988, Hart and Scheibling 1988, changes in larvae ofthe asteroid Luidiafoliolata Strathmann et at. 1992) . McEdward (1986) b) duration ofthe larval developmental period and Strathmann et at. (1992) suggested that and c) juvenile size at metamorphosis. this is an adaptation to variable food supply.

297 MATERIALS AND METHODS

Adult Luidia foliolata were collected from Bellingham Bay, Washington on the 1st of April 1992. On the 4th ofMay 1992 spawning was induced by intracoelomic injection of 10 4 M I-methyladenine. Diameters of 20 unfer tilized eggs from a single female were mea sured. The remaining eggs were fertilized with sperm from a single male. Fertilized eggs were Stage ii Stage iii distributed into three replicate jars per treat ment, each containing 2 liters of 0.45~m fil tered sea water and 600 larvae initially. Jars were stirred by a systemofmotor driven paddles (Strathmann, 1987) and kept at ambient sea temperatures by immersion in baths supplied by the laboratory's sea water system. Tempera ture varied from 14°C at the start ofthe experi ment, to 16°C in August, then dropped to 10°C at the end of the experiment in December. The sea water was changed every two days and food added. For the high food ration, Stage iv Stage v larvae were fed Dunaliella tertiolata at a con centration of 5000 cells/ml at the start of the experiment; this was increased to 10,000 cells/ ml 31 days after fertilization. For the low food +----- A ration, larvae were fed 500 cells/ml at the start of the experiment; this was increased to 1000 """":PPl-+--\---- B cells/ml 116 days after fertilization. The con centration oflarvae was reduced similarly in all +--I--t--- C jars as they were sampled equally without replacement for measurements of larvae. -- D Every two days, samples of larvae (5 to 1------E 10 per replicate) were relaxed in a.33M MgClz ~----F for 5 to 10 minutes and then fixed with 4% Stage vi Stage vii formaldehyde with CaC03 buffer. Measure ments were made with an ocular micrometer. The developmental stages examined include i) Figure 1: Schematic diagram ofstages of devel bipinnaria with coelomic pouches at the level opment, based on the digestive system, the of the mouth, ii) coelomic pouches above the coelomic pouches and the rudiment ofthejuve mouth, iii) coelomic pouches in contact, iv) nile. A) coelomic pouches fused B) mouth C) coelomic pouches fused, v) appearance of the esophagus D) stomach E) hydrocoel lobes F) rudiment, vi) dorsal median process and ven definitive star (juvenile rudiment). tral median process well separated and ofsimi lar length and definitive star clearly seen (see

298 39d 42d 6sd

,! 'W PRL

2sd

ro 39d to 2sd 42d 6sd to

Figure 2: The fifteen-day-old bipinnaria is an example of an initial feeding stage for both food rations, AL, anal lobe; PRL, preoral lobe. Bipinnaria in the same row had the same food ration (high, top row; low, bottom row). Bipinnaria in the same column are the same age. Age is in days after fertilization. All bipinnaria were preserved and photographs are at the same scale of magnification. Figure 1). At the advanced bipinnaria stage, the 1100 A length of preoral arm and anterior dorsal ann 1000 were measured as well as total larval length (see 900 Figure 5). The diameter ofjuveniles was mea 800 .c:...... sured, d1 being the greatest diameter and d2 the ~700 ~ least. ..-< ~ 600 Variations due to differences among jars o E- 500 were tested using analysis of variance for un • High food 400 equal sample sizes (Sakal and Rohlf 1981). o Low food Anova's were conducted for three replicates 300 per treatment at the start of the experiment and 200 -+---.-----r-r--~~____r---,.-.__-.--_, 200 300 400 500 600 700 for two replicates per treatment towards the Total width middle of the experiment due to loss of a 550 B replicate at each of the high food and the low •••00 food rations. No differences were observed 450 o· among jars. All jars per treatment were then o -5 o combined. The assumption of homogeneity of ~350 ~ variances between treatments was satisfied and .c: u C':l transformation of the data was unnecessary. E 250 ...... o (/) 150 RESULTS

50 -+----,.--r----,.--r--,r---r-_,r-_, 200 300 400 500 600 The diameters ofunfertilized eggs from a single Total width female was 144.3+6.9 urn and for fertilized 450 C .c: eggs including the fertilization membrane, u g 400 o 158.5+9.9 urn, (means of 20 eggs each). 0.. .-U o E s: 350 Divergence in form ~ o u ~ ..::: ... ~ 300 o No morphological differences were ob ' o ~o served for larvae from a single pair of parents .c:...... ~250 kept at two food rations till 39 days after fertili j ~ zation. The shape of the preoral and anal lobes 200 -+----,----,--r-.,.---r----,----,.-.__-.--_, of larvae maintained at the two food rations 50 150 250 350 450 55 0 differed (Figure 2). As the arms developed a Len gth of digestive tract difference in the shape of the arms was also Figure 3: Dimensions ofbipinnaria developing observed. Larvae at the high food ration had at a high and low food ration. All measurements arms with pointed ends and those at the low are in microns. A) Total larval length versus food ration had arms with rounded ends (i. e. total larval width. B) Stomach length versus more lobular arms), (see Figure 2: 39,42, 65 total larval width. C) Length ofthe left coelo days). mic pouch versus length of digestive tract.

300 Total larval width relative to total larval fertilization (Figure 2 and Figures 4A to 41). 1 ngth, total larval width relative to stomach After this, growth rates of all measured body length, and the length of the digestive tract parts w re slower for the low food ration. No relative to the length ofth left coelomic pouch growth in length was observed and that in did not differ betwe n food rations (Figure 3A width decreased and remained low until 75 to 3C). days after fertilization. Growth ofthe digestive tract slowed and the width of the stomach Growth of body parts decreased andremained low up to 80 days after fertilization for larvae at the low food ration Similar larv I siz s (growth in total (figure 4IJ and 4G). tomach width also de length, total width, post oral lobe, digestive creased initially for those at the high food tract, length of right and 1 ft coelomic po uches, ration but after 40 days a rapid increase in the length and width of th st mach, and the width width of the stomach was observed for these of the m uth) were obs rve for larvae main bipinnariae. tained at the tw food ration until 35 days aft r

1100 A ~900 t:: ~ ~ 700 -J • High food ~ 500 o Lo w food 300 -t-...... -...... -..,...... -..,...... --r---r--..----. o 40 80 120 160 40 80 120 160

,.. ~750 D "5:;) 600 E -5 600 F t:: ~ 650 8.500 8. 500 u 400 ~ 550 '§400 0 300 '§ 300 ~ 450 'B ';:l u 200 'B200 ~ u 350 ~ 1 00 OJ) .c 100 OJ) ~ 6 250 ~...,..-__r____r__..._..._-r--r-....., (:2 O-+--.----,.--r---r----.-----. ~ O -t---r------,- ..,...... -----r----r-----. o 40 80 120 160 0 40 80 120 o 40 80 120 o 250 270 I 200 G -5 H ~ ~ 2 20 180 "- 0 0 ~ 200 ... 0 0 0 ~ '~ ' ~ 160 .- ...c: ~ . 0 00 u ...c:u 150 -5 170 E140 o=' ~&CO 0 ~ 9 120 ....8 100 120 (/.) if) EB (/.) I00 -t--r--...---r---r----r----r----r----. 50.:+--...... -.,.-..,...... -..,...... -r--r--r----, 70 --t--'-""r-..._...--r---r----r----r---, o 40 0 120 160 o 40 80 120 160 o 40 80 120 160 Days aft r fe rtilization Days after f rtilization Days after fertili zati n

Figure 4:Growth of b y parts of bipinnariae fed high and low food ration. All m asurements are in microns. ) Total larval length. B) Total larval width. C) Post oral 1 be. D) Length of the dige tive tract. E) Length of right coelomic pouch. F) Length of 1 ft coelomic pouch. G) Stomach width. H) Stomach length. I) Width of lTIOUth.

301 Development rates Table 1. Duration of a stage for bipinnaria larvae of Luidia foliolata maintained at high During the development ofthe coelomic and low food rations. (Stage VII refers to the pouches and during the early stages ofrudiment first day when advanced stage bipinnaria were development, bipinnariae at the low food ration observed to the first day when juveniles ap took longer to get to a new stage, the time spent peared, the other stages refer to the first day in a given stage was twice to three times as long when stage appeared to the day when last seen. thanfor those maintained at the high food ration Stage II ill IV V VI vn (Table 1). Stage 1 bipinnariae were present up to 25 days after fertilization in cultures fed the Ration high food ration and up to 99 days after fertili zation for cultures fed the low food ration. High food 19 33 32 19 17 20 Stage2 bipinnarialarvae appeared 39 days after fertilization for those maintained at high food Low food 69 56 56 49 42 26 ration and 65 days after fertilization for those maintained at low food ration. As bipinnaria progressed through the different stages, the the cultures to the first day when a juvenile time spent at a given stage tended to decrease. appeared) was only 6 days longer (26 days) for The duration of stage vii (the advanced larvae at the low food ration than for those bipinnaria stage, estimated to be the first day maintained at the high food ration (20 days). when advanced bipinnariae were observed in

OM A B v P

o PLA 30 ~m

Figure 5: Advanced bipinnariastage(as definedin text). A) High food (106 days afterfertilization). B)Low food (169 days afterfertilization). ADAantenordorsal arm; D, definitive star; DMP, dorsal median process; PLA, posterior lateral arm; PRA, preoral arm; VMP, ventral median process.

302 . A Advanced bipinnaria larvae and Metamorpho ,.-., 2000 - 8 . SIS ::l '-' 1800 ..c: ~ Larvae maintained at the low food ration -5 1600- took twice as long to get to the advanced -~ bipinnaria stage (competent stage for metamor C 1400 ~ phosis) but were larger and had longer arms - than those from the high food ration (Figure 5 ~ '. High food - 1200- '0 and 6). For both food rations, larvae that got to ~ . a Low food the advanced bipinnaria stage later tended to be 1000 -+---r_.,..------r-_.....--=::::::::;:::===;::::::::::=::::::;:::====;---I I I I I 60 100 140 180 bigger (example for the low food ration, ad Days after fertilization vanced bipinnariae observed 141 days after ,.-., fertilization had a total larval length of1238+39 S urn compared to those observed 192 days after 6 600 B S fertilization which had a total larval length of ~'"' 1998+ 84 urn (Figure 6A, B and C). However, -~ 500 no significant differences in the length of the e'"' arms among days within a food ration was "'0 .-5400 observed (length ofpreoral arm; high food, p = '"'~ 0.1, df = 54; low food, p = 0.4, df = 27; length ....e ~ of anterior dorsal arm; high food, p =0.08, df= ~ 300 o 54 ; low food, P = 0.5, df = 27). All advanced ..c:.... bipinnariae at a given food ration were pooled gf 200 -T-----,.-....,-----,.-....,-----,r--...,....-_....------. and a simple ANOVA carried out. Significant ~ 60 100 140 180 220 differences in total larval length, length of the Days after fertilization preoral and anterior dorsal arm were observed between food rations, figure 6A, 6B and 6C (p 600 c S =0.0001, df = 82 for total length, preoral arm, '"'~ and anterior dorsal ann length respectively). -E500 Juveniles started appearing 85 days after o ~ fertilization at high food ration and 167 days 0.400'"' after fertilization for those at low food. A total ~e ..c of 78 juveniles was produced for those at the ~300 high food ration and only 18 for those at the low ~ ..J food ration. The diameters (dj and d2) ofjuve niles produced did not differ significantly be 200 -T-----,.-....,-----,.-....,-----,-...,....----,....-----, urn, 60 100 140 180 220 tween food rations (high food, 602+53 Days after fertilization 560±75 urn, N = 43; low food, 599+66 urn, 563+80 urn, N = 18). Figure 6: Growth in A) total larval length B) the length of the anterior dorsal arm C) and the DISCUSSION length of the preoral arm for advanced stage larvae at high and low food ration. The amount offood available did not influence

303 larval growth and development during the first Larval arms tended to be more pointed at the 35 days for the asteroid Luidiafoliolata. Simi high food and more rounded at the low food lar results were obtained for the asteroid Luidia ration. At the advanced bipinnaria stage nutri clathrata (George et al. 1991), and other aster ents were allocated to an increase in the length oids (Olson et al. 1987). Contrary to these of the larval arms rather than into growth of the results, echinoid larvae are known to respond rudiment. Many studies (Strathmann 1971, immediately to low food supply by increasing 1987, Fenaux et at. 1988, Hart 1991) have the length ofthe larval arms (Strathmann et al., indicated that an increase in arm length results 1992, Biodron-Metairon, 1988, Hart and in a longer ciliated band and higher clearance Scheibling, 1988 and George, 1990). This rates. McEdward (1984), Hart and Scheibling difference might be due to the difference in the (1988) suggested that shape change might lead form of plutei and bipinnaria larvae. The fact to maximum clearance rates. Thus ina food that the appearance and growth of the larval limited environment bipinnariae might require arms occurs much later for these bipinnariae an increase in arm length to increase their (58 days after fertilization at a temperature of capacity to capture food particles. This would 13°C for Luidia foliolata, present study) than ensure that sufficient material is accumulated for plutei (2 days after fertilization at a tem for the developing rudiment in the shortest perature of 20°C for Arbacia lixula, George, possible time. In the present study, accumula 1990) might also explain the differences ob tion of sufficient material might have been served. further enhanced by the reduction in the num Strathmannetal. (1992) emphasizedthat ber of bipinnariae in the jars due to sampling body parts may functionally serve only the and natural mortality. As Strathmann et al. larva (eg, larval arms), both the larva and the (1992) point out, the question is not whether postmetamorphic juvenile, (eg. the cells of the high food rationproduces faster growth through gut which are rich in lipid dissociate and subse metamorphosis but whether the type of mor quently reorganise to form the cardiac portion phogenesis produced by a given ration is the of the adult gut, Burke, 1981, 1989), or only the one that produces the shortest precompetent postmetamorphic juvenile, (eg. the rudiment). larval period at that ration. The time when these structures appear and the Changes in shape and length ofthe larval size ofthese different structures depends largely arms might be due to, organic materials re on the species considered and the amount of leased by algal cells, not differences in food food available to parent and offspring (George, ration (Strathmann et al., 1992). Some filtrates 1990). For echinoids growth is allocated to from algal cultures affect larval form (Wilson, increase in the length of the larval arms when 1981). In the present study only the quantity of food is scarce and to cells that are carried Dunaliella tertiolata was changed, different through metamorphosis whenfood is abundant results might be obtained using another algal (Strathmann et al. 1992). When food was species. The results however agree with those scarce growth of the digestive tract slowed, obtained by Boidron-Metairon (1988), Hart bipinnariae spent twice to three times longer in and Scheibling (1988) and Strathmann et al. a given stage, and metamorphosis occurred 167 (1992) on developmental plasticity in plutei days after fertilization. that experienced only quantitative changes in Different food rations led to different food supply. larval shapes for the asteroid Luidia foliolata. The diameter ofjuveniles produced did

304 not differ between the two food rations. In a ACKNOWLEDGEMENTS food limited environment, the cost associated wi th an increase in the duration of the I thank all those at Friday Harbor Labo precompetent period (during which shape ratories and Harbor Branch Oceanographic change ensures that enough material is accu Institution who helped in various ways to make lTIU lated to maintain a constant metamorphic this study successful. I thank especially C. size) might outweigh that associated with the Staude and J. Murray who collectedthe seastars. production ofvery smalljuvenilesfor the seastar R. Strathmann and M. Strathmann suggested Luidiafoliolata. The production of very small this project and read earlier versions of this juveniles might be a disadvantage if food is manuscript. Craig Young and Tom Smoyer scarce and lead to an increase in vulnerability helped rne prepare the photographs. This study to predators (Andrew and Choat, 1982 ~ An was supported by postdoctoral fellowships from drew and Underwood, 1989). Friday Harbor Laboratories, University of In the present study larvae were main Washington and Harbor BranchOceanographic tained at low food ration for over 190 days. It Institution. This is HBOI contribution number is possible that dissolved organic matter and 1014. bacteria (Shilling and Manahan, 1990, Manahan, 1990) were used by Luidiafoliolata REFERENCES in addition to the algal food supplied during larval development. JaeckJe and Manahan Andrew, N. L. & Choat. J. H. 1982. The influ (1992) indicated that the total amount of dis ence of predation and conspecific adults on solved organic matter in sea water is altered by the survivorship of juvenile Evechinus the methods employed in filtering seawater in choroticus (Echinoidea: Echinometridae). the laboratory. Sugimura and Suzuki (1988) Oecologia (Berlin). 54 : 80-87. noted that the concentration of dissolved or Andrew, N. L. & Underwood, A. 1. 1989. ganic substances in the sea is very high. In Patterns of abundance of the sea urchin natural seawater with Jaw phytoplankton con Centrostephamis rodgersii (Aggassiz) on centrations larvae ofthe asteroid Luidiafoliolata the central coast ofnew south Wales,Austra might be able to absorb and metabolise dis lia. 1. expomar. Biol. Ecol. 131 :61-80. solved organic substances and develop faster Boidron-Metairon, I. F. 1988. Morphological than those kept in the laboratory with a low plasticity in laboratory-reared echinoplutei food supply. ofDendrasterexcentricus (Eschscholtz) and To summarise, different food concentra Lytechinusva riegatus (Lamarck) in response tions led to larval arms with either rounded or to food conditions. 1. expo mar. Bioi. Ecol. pointed ends, and longer arms for Luidia I 19 : 31-41. foliolata. This indicates that, like the echi- Burke, R. E. 1981. Structure of the digestive noids, sorne asteroids might have the ability to tract of the pluteus larva of Dendraster produce bipinnariae with alternative forms of excentricus (Echinodermata: Echinoidea). morphology in response to variation in food Zoomorphology 98: 209-225. supply. Burke, R. E. 1989. Echinoderm metamorpho sis: Comparative aspects of the change in form. Echinoderm studies. Jangoux, Mand Lawrence, J. M. (eds.) Rotterdam, Nether-

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