Sexual Dimorphism in Four Species of Rockfish Genus Sebastes (Scorpaenidae)
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181 Sexual dimorphism in four species of rockfish genus Sebastes (Scorpaenidae) Tina Wyllie Echeverria Soiithwest Fisheries Center Tihurori Laboratory, Natioriril Maririe Fisheries Service, NOAA, 3150 Paradise Drive) Tibirron, CA 94920, U.S.A. Keywords: Morphology, Sexual selection. Natural selection, Parental care. Discriminant analysis Synopsis Sexual dimorphisms, and factors influencing the evolution of these differences, have been investigated for four species of rockfish: Sebastcs melanops, S. fluvidus, S.mystiriiis. and S. serranoides. These four species, which have similar ecology. tend to aggregate by species with males and females staying together throughout the year. In all four species adult females reach larger sizes than males, which probably relates to their role in reproduction. The number of eggs produced increases with size, so that natural selection has favored larger females. It appears malzs were subjected to different selective pressures than females. It was more advantageous for males to mature quickly, to become reproductive, than to expend energy on growth. Other sexually dimorphic features include larger eyes in males of all four species and longer pectoral fin rays in males of the three piscivorous species: S. rnelanops, S. fhvidiis. and S. serranoides. The larger pectoral fins may permit smaller males to coexist with females by increasing acceleration and, together with the proportionately larger eye, enable the male to compete successfully with the female tb capture elusive prey (the latter not necessarily useful for the planktivore S. niy.ftiriiis). Since the size of the eye is equivalent in both sexes of the same age, visual perception should be comparable for both sexes. Introduction tails (Xiphophorus sp.) and gobies (Gobius sp.) as fin variations, in guppies (Paecilia sp.) and wrasses Natural selection is a mechanism of evolution (Labrus sp.) as color variations, in eels (Anguilla which can influence physical characteristics of a sp.) and mullets (Mugil sp.) as size differences. and species, characteristics which reflect selective pres- in silurids (Oinpok sp.) (Rao & Karamchandani sures in the species environment. Sexual selection 1971) and sculpins (Myoxocephalus sp.) its mor- is a component of natural selection that acts inde- phological variations in body proportions (Breder pendently upon males or females. Sexual dimor- & Rosen 1966). phism can result from either component. In fishes, secondary sexual dimorphisms are Sexual dimorphisms, which occur in every major often associated with species that have internal group of vertebrates, are commonly manifested in fertilization or protection of the eggs or young by a mammals as size differences, in birds as color varia- parent (Breder & Rosen 1966). Despite the wide- tions, in reptiles as defensive structures, and in spread relationship between internal fertilization amphibians as sounds. Fishes of both fresh and salt and secondary sexual dimorphism, one of the most water also exhibit sexual dimorphisms: in sword- speciose groups of live bearers in the northeast Pacific Ocean, the rockfishes (L~chasrr.s)with ap- cal differences between the sexes of any one species proximately 70 species occurring in that region. that could be used. in themselves. to characterize docs not show obvious sexual dimorphisms. the sexes. and (3) if there are differences. what Four species of Sc~hrrcrc~s\vex xtudied: S. their significance might be. ITIPIN~IO~S.the black rockfish: S. ,f%c~.cdus,the yel- Working within the definitions of selection that lowtail rockfish: S. /TzJ.sriiirrs. the blue rockfish: and hwc been rnade here. an attempt will be niitde to 5. .\err.rrrwirlc.s, the olive rockfish. All four species discern which coniponent - natural or sexual selec- are very similar in body shape and size. ivith con\ ci tion- ma! ha\e exerted the greater influence in any interorbital spaces. weak head spines and ;I dusky sexually dimorphic feature found in these four spe- olive-to-black coloration. all key characters used in cies of .Sehrr.rtr.s. Natural celection will be credited the identification of rockfish (Miller K: Lea 1970). for those features that primarily affect the survival Similarities include morphologies and reproduc- of thc entire species, while sexual selection will be tive characteristics while they are seixiratcd ecolo- limited to those features'that affect the reproduc- gically by different diets. feeding times. and depth tive advantage of one individual over another. distributions. These four species have heen studied more than other rockfish because they comprise ;t large part of the commercial ,ind sport-fishing land- Methods ings. and iire readilq accesible in large aggrega- tions near shore. Rockfish were collected throughout 1977 from In Sc1~~c.sthe contribution to thc siirvi\,aI of three localities along the coast of central Califor- young is priniaril? accomplished by the female. nia: Point Reyes. the Farallon Islands. and Cordell Fertilization is internal with possible storage of Bank (Fig. I). These localities lie at the cornersofa sperm by the female (Sorokin 1967). During geAta- triangle covering roughly 250 square miles. This tion the arterial suppl!, to the gonad serves for the relatively limited area was chosen because Miller & exchange of metabolic wistc\ (Moser 1967) and the Geibel (1973) showed that growth rates in blue ovarian fluid provides some nutrition for the de- rockfish from widely sepxated geographic areas veloping cmbroys (Boehlert & Yoklavich 1984). differed. Fish used in the morphometric study were Fecundity wries among \peck\. but is aln ;I>S collected as part of a survey of age and length in the large. increasing with the size of the fcniale (Phi- rockfisheb of central California (Sen 19S.1). and llips 1964. Boehlcrt et ill. 19x3). with some species constitute a subsarnple of the fish used in that sur- possibly having two brood\ per year (Moser 1007. \.e!'. MacGregnr 1970). In Sdmctc.s. selection ha\ fa- vored increasing reproductive success 13)- means of large females capable of producing and acconi- modating large numbers of enibr!os. I-h c on1 y reports of morph ol ogi cii 1 d i ffe re n ce s 3S0N between sexes of Schrrste.s ;ire pro\,ided by Chen (Iq7l) and Moser (1967). Chen fouild sexual dinior- phism in Schtrstes I~//I~UISI~.S.with males having a shorter prc-iinal length but ;I greater ;inn1 haw. upper length. anal ray length. snout length and 0 10 20 prepelvic length (f'<O.Ol). Moser noted differen- ces in t ti e LI rog c nit ii 1 papi I I ;i of Schri.\ 10 dot I I I I I I 1 purrci.~pi/ris.In this inve\tigaticm body measurc- 123W mentb taken from four spccics of rockfish ha\ e brcn analyzed to determine (1) if Chen's findings are more widespi-e:itl. (7)if thcre are n1o1qJliolc;p 183 Specimens were collected from the hook-and- tinued beyond the ages obtained in previous stud- line sportfishing fleet. Fish were filleted on board ies. the fishing boat. and the carcasses were collected The average length of the males and females at and handled in a standardized way to reduce the each age was used to compare growth rates be- variability in measurements which occurs between tween the sexes. The comparisons were made from whole fish and carcasses or fresh and frozen fish all fish sampled (Table 1). (Forrester 1967). In the laboratory the otoliths Sex and the stage of gonadal development were (Sagitta) were collected, the gonad state was deter- determined in the laboratory. Sexes were identi- mined. and 23 body parts. in addition to standard fied by gonadal inspection: ovaries were charac- length, were measured. terized by an egg mass encased by the ovarian wall Ages of the four species were determined by while the testis were characterized by appearing counting one opaque and one translucent zone of solid in cross-section. Ovaries were classified as: the otolith. Annular growth increments were vali- immature, with developing eggs. eggs containing dated up to 12 years in the black rockfish by Six & eyed embryos or spent. Testis were classified as: Horton (1977), up to 12 years in the yellowtail immature, undergoing spermatogenesis, or spent. rockfish by Kimura et ai. (1979), and up to 4 years Gonad states of specimens collected throughout in the olive rockfish by Love bt Westphal (1981). the year were used to determine the reproductive Ages of blue rockfish have been determined from seasonality. scale annuli and comparison between the growth Morphometric measurements were made with zones of the otoliths and scales showed similiar vernier calipers (+0.01 mm) on freshly thawed fish patterns (Miller & Geibel 1973). All researchers carcasses. The 24 body parts measured included: agreed that, for the ages studied, one opaque and total length, fork length, standard length. head one translucent zone are deposited per year. Fish length. length of the base of the anal fin, snout collected in this study also included individuals length, interorbital width, width of the orbit, older than those from previous studies and it was length of the upper jaw, lower jaw projection. assumed the reliability of the annual marks con- width of the pectoral tin base. longest pectoral fin TXik/. Mc;iri st;riitliird Iciigfh (mm)iit iigc for rn;rlc\ (hl) ;rnd lcniiilcs (Fj in Ioiir \pecics 01 rochfish collccted during 1077. Numhera (N) 01 indi\idu;ils u\cd ICI ~;iI~iiliitcIcnsth in parcnthcses. Agc (!I-) .s. ,ticlliriop.\ s. //ol~ir/irc s. lliv\/;~lii\ s. cc~r.rtrlroitlcr M (N) F (N) M (N) F (N) M (N) F (N) M (N) F (N) 4 283 (4) 235 (4) 227