Flexible Reproductive Strategies in Tropical and Temperate Sepioteuthis Squids
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Marine Biology 02001) 138: 93±101 Ó Springer-Verlag 2001 G. Pecl Flexible reproductive strategies in tropical and temperate Sepioteuthis squids Received: 11 May 2000 / Accepted: 12 September 2000 Abstract A major diculty confronting the determina- distinct seasonal dierences in the reproductive biology tion of cephalopod reproductive life history is assessing of S. australis. Summer-caught individualshad much over what portion of the life span an individual is higher gonadosomatic indices and may have been laying reproductively mature and actively depositing eggs. This larger batchesof eggscompared with winter-caught paper assesses the potential of the tropical Sepioteuthis individuals. Summer-caught females also showed a lessoniana and two genetic typesof the temperate negative correlation between egg size and egg number Sepioteuthis australis, to spawn multiple batches of eggs within the oviduct, suggesting that some individuals at discrete times throughout the adult life span. This is were producing fewer, larger eggsand othersmany achieved by histological examination of the ovarian smaller eggs. Evidence suggests that considerable ¯exi- gametogenic cycle and detailed morphological assess- bility isinherent in the reproductive strategyof both ments of the reproductive system, in conjunction with S. lessoniana and S. australis. other biological information. The genetic type of S. australis found at the northern limitsof itsAustralian distribution showed evidence of a high correlation Introduction between body size and quantity of mature eggs, sug- gesting that eggs may be accumulating to be laid in a An individual's or population's ``®tness'' in the evolu- single batch. Although maturation was also a size- tionary sense is determined by both absolute fecundity related process in S. lessoniana and Tasmanian S. aus- and generation interval 0Ro 1986). Both of these life- tralis, oviduct size was not correlated with body weight history traits are dependent on the reproductive strategy in mature females, which is indicative of multiple of a species, and indeed are likely to be divergent spawning. Further supporting evidence includes rela- between those species or individuals that breed once and tively low gonadosomatic indices, the heavier weight of die, and those that breed over an extended time frame. the ovary relative to the oviduct, and the feeding activity Optimal age or size at maturity, and the associated age- of mature animals. Mature S. lessoniana and S. australis and size-speci®c schedules of reproductive investment, individualswere presentat each location over very wide are just some of the life-history characteristics that are age and size ranges. In Tasmanian waters, there were also intimately related to the reproductive strategy of a species 0Stearns 1977). As a consequence of the very short life span typical of most cephalopods, annual recruitment is essential to sustain populations 0Boyle Communicated by O. Kinne, Oldendorf/Luhe 1990), and as such an understanding of the reproductive strategy of a cephalopod ®sheries resource is crucial. G. Pecl Determining how long an individual takesto com- School of Marine Biology and Aquaculture, James Cook University, Townsville, plete egg maturation and deposition, and assessing what Queensland 4811, Australia portion of the life span this period represents, is a major diculty confronting detailed examinationsof cephalo- Present address: pod reproductive biology in ®eld populations0Collins Marine Research Laboratories, et al. 1995b). Although coleoid cephalopodshave tra- Tasmanian Aquaculture and Fisheries Institute, University of Tasmania, GPO Box 252-49, ditionally been viewed as semelparous organisms that Tasmania 7053, Australia reproduce once and die 0Arnold and Williams-Arnold Tel.: +61-3-62277277; Fax: +61-3-62278035 1977; Calow 1987; e.g. Illex illecebrosus, O'Dor 1983; e-mail: [email protected] Todarodes paci®cus, Okutani 1983), it isincreasingly 94 apparent that many species are not restricted to this mation on the temporal patterns of spawning intensity. strategy. Reproductive strategies that involve spawning Extended spawning seasons tend to be associated with within one season only but in which reproductive eort multiple spawning 0Lum-Kong et al. 1992; Porteiro and is distributed over space and time over a portion of the Martins1994); however, it isoften unclear if prolonged life span are now known to be common among cepha- spawning is due to extended individual spawning or lopods0Villanueva 1992; Hun Baeg et al. 1993; Wada asynchronicity in the population 0Boyle et al. 1995). and Kobayashi 1995; Gonza lez and Guerra 1996; This paper uses a combination of histological and Maxwell et al. 1998). morphological assessment measures, in conjunction with In species with non-asymptotic growth patterns, other biological information, to assess the reproductive growth and reproduction necessarily proceed together strategies of the tropical S. lessoniana from two locations over much of the life cycle, and it islikely that the in northern Australian waters and the temperate S. aus- diversity of spawning modes is related to growth pat- tralis from two locations in southern Australia. An terns0Mangold et al. 1993). In general, the growth and examination of the patternsin egg maturation between life spans of tropical and temperate species dier. seasonal extremes was also conducted for S. australis at Temperate and subtropical loliginids live for approxi- the most southern location. Recent research has dem- mately 1 year 0Natsukari et al. 1988; Collins et al. onstrated that S. australis from the two regionsexam- 1995a) or 2 years0Hanlon et al. 1989), whereastropical ined in this study constitute two distinct genetic stocks species have life spans of <6 months 0Jackson 1990; 0Trianta®llos and Adams, in press). Dierences in the Jackson and Choat 1992; Jackson and Yeatman 1996). reproductive biology have been put forward asa reason There is, however, little information about how the to support the hypothesis of these two genetic types as spawning biology of closely related species from dispa- distinct taxa, so the examination of regional dierences rate temperature zonesmay dier. Within a population in the reproductive biology of S. australis isparticularly the growth characteristics of cephalopod species are pertinent. highly plastic, with small changes in temperature pro- ducing large changesin growth ratesand ®nal size 0Forsythe 1993). Consequently, in cephalopod popula- tionswhere spawning takesplace all year round there Materials and methods may be seasonal in¯uences on age- and size-speci®c schedules of reproductive investment and subsequent Collection and processing patternsin egg maturation and deposition. Sepioteuthis lessoniana individualswere obtained from waters Sepioteuthis lessoniana and S. australis are both adjacent to Townsville 0Table 1) by jigging, and from Brisbane by a relatively large, neritic squids of commercial importance combination of tunnel-netting by the commercial sector and in Australia. The maximum life span of S. lessoniana jigging. S. australis wasobtained in Newcastleby jigging, and in Tasmania by a combination of jigging and modi®ed purse-seine. in Australian tropical and subtropical waters is The 196 femalesfrom Tasmaniaincluded 42 femalescaught during 6±7 months0Jacksonand Choat 1992). S. australis winter and 154 caught in summer. achieves a similar life span of around 6±10 months in Most individuals were refrigerated or placed on ice within a few temperate waters 0Pecl, unpublished data). Both these hours of capture and processed within 12 h. Some individuals species show rapid growth 04±8% body wt day)1) obtained from the commercial sector had been frozen: 37 from Brisbane, 24 from Townsville and 10 from Tasmania. Dorsal during their short life spans. mantle length 0ML) was measured to the nearest millimetre and The mature eggsof Sepioteuthis spp. are very large total body weight to the nearest 0.01 g. The mantle muscle, ovary, compared to those of other squids 0Hanlon 1990), in the oviduct, nidamental and oviducal glands were dissected out and range of 5±10 mm. Large eggscannot be matured all at weighed separately. A gonadosomatic index 0GSI) was derived for each individual asfollows: once, and S. lessoniana isknown to have the capacity, at least in the laboratory, to lay multiple batches of eggs OW NW ODW OV GSI over a signi®cant portion of the life span 0Wada and BW À RW Kobayashi 1995). Back-calculated hatching dates of both S. lessoniana and S. australis 0Pecl, unpublished where OW ovary weight, NW nidamental gland weight, ODW oviducal gland weight, OV oviduct weight; BW total data) suggest that hatching, and consequently spawning, body weight and RW total reproductive weight 0combined take place all year round, although there islittle infor- weight of ovary, oviduct, nidamental and oviducal glands). Table 1 Sepioteuthis lessoniana and S. australis. Sample sizes, Species, location Location Collection dates Total No. of collection locationsand dates sample size females S. lessoniana Townsville 19°10¢S; 146°55¢E Feb 1995±Oct 1997 116 50 Brisbane 27°20¢S; 153°3¢E Aug 1995±Apr 1997 173 83 S. australis Newcastle 32°45¢S; 152°10¢E Aug 1995±Dec 1995 131 51 Tasmania 42°15¢S; 148°10¢E Jan 1996±Jul 1997 493 196 95 Weightscould not be measuredfor 12 S. lessoniana caught in from both locations were combined to simplify analyses. Townsville; however, total body weight was estimated for these from Early stage S. lessoniana femaleswith