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This study investigates the reproductive strategies of the pill-box crab, Halicarcinus cookii on the Kaikoura Peninsula, New Zealand. Various aspects essential to understanding reproductive strategies were examined including growth, population dynamics, reproductive biology and mating behaviour. H. cookii exhibits obvious sexual dimorphism such that females develop wide abdomens forming brood chambers, and males tend to grow larger than females and have larger chelipeds in relation to body size. H. cookii allocates energy into growth and reproduction in separate phases of its life cycle where growth ceases as reproductive maturity begins due to a terminal/pubertal moult. Despite the presence of ovigerous females throughout the 15 month sampling period, the population was highly seasonal, with peaks in recruitment and growth occurring primarily during the winter months and peaks in numbers of mature individuals during the summer months. Reproductive output increased with body size in H. cookii, as larger females produced more eggs and larger males transferred more sperm than their smaller counterparts. Ovaries matured prior to the terminal/pubertal moult (anecdysis) and, in multiparous females, in synchrony with brood development, allowing females to produce broods in quick succession, maximising their reproductive output in their short life span (approximately 12-18 months, 6 months as an adult). Incubation duration of broods decreased as seawater temperature increased, suggesting that temperature is the primary cause of the seasonal population cycling. Sperm storage allowed females to produce at least 4 fertilised broods without re-mating. Some sperm mixing in the spermathecae appeared to occur and the ventral-type structure implies last male sperm precedence. Males therefore preferentially mated with females closest to laying a new brood and guarded them longer than other females to ensure their paternity. Guarding duration varied according to the sex ratio allowing males to maximise their reproductive output.

This study investigates the reproductive strategies of the pill-box crab, Halicarcinus cookii on the Kaikoura Peninsula, New Zealand. Various aspects essential to understanding reproductive strategies were examined including growth, population dynamics, reproductive biology and mating behaviour. H. cookii exhibits obvious sexual dimorphism such that females develop wide abdomens forming brood chambers, and males tend to grow larger than females and have larger chelipeds in relation to body size. H. cookii allocates energy into growth and reproduction in separate phases of its life cycle where growth ceases as reproductive maturity begins due to a terminal/pubertal moult. Despite the presence of ovigerous females throughout the 15 month sampling period, the population was highly seasonal, with peaks in recruitment and growth occurring primarily during the winter months and peaks in numbers of mature individuals during the summer months. Reproductive output increased with body size in H. cookii, as larger females produced more eggs and larger males transferred more sperm than their smaller counterparts. Ovaries matured prior to the terminal/pubertal moult (anecdysis) and, in multiparous females, in synchrony with brood development, allowing females to produce broods in quick succession, maximising their reproductive output in their short life span (approximately 12-18 months, 6 months as an adult). Incubation duration of broods decreased as seawater temperature increased, suggesting that temperature is the primary cause of the seasonal population cycling. Sperm storage allowed females to produce at least 4 fertilised broods without re-mating. Some sperm mixing in the spermathecae appeared to occur and the ventral-type structure implies last male sperm precedence. Males therefore preferentially mated with females closest to laying a new brood and guarded them longer than other females to ensure their paternity. Guarding duration varied according to the sex ratio allowing males to maximise their reproductive output.

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第21334号 / 理博第4430号 / 新制||理||1636(附属図書館) / 京都大学大学院理学研究科生物科学専攻 / (主査)教授 古市 剛史, 教授 湯本 貴和, 教授 髙井 正成 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM

Synalpheus shrimp species of the gambarelloides group are the only marine organisms displaying the highest level of social functioning, eusociality. Their social hierarchies are equally complex compared to the reproductive abnormalities that have been recently discovered. For instance, snapping shrimp of the genus Synalpheus were thought to be gonochoric, i.e. developing as independent sexes, until scanning electron microscopy studies revealed intersexed gonopores in several species. This project analyzed both the species composition, and accompanying reproductive structures, of Synalpheus spp. (Caridea: Alpheidae) comprised of densely aggregating communal and pair-living colonies in the Florida Keys, Florida. Colonies of pair-living and communal Synalpheus spp. were observed from hosts Spheciospongia vesparium and Spongia sp. from hard bottom assemblages of the Florida Reef Tract in order to assess differing population structures. Comparisons were made of the measures of overall and relative abundance, frequency by species and sex category, and variation in growth by species and sex category, for each individual colony. We then used scanning electron microscopy (SEM) images to determine the secondary sexual characteristics of three species (Synalpheus brooksi, S. herricki, and S. cf. herricki) which range in social behavior. Species were widely consistent in both host choice and distribution, across all sampling areas. The abundance of communal species Synalpheus brooksi was much greater than expected at all sites, in comparison to previously published work. While Synalpheus longicarpus was reported at higher frequencies in prior studies, our results yielded a much lower frequency of this species, often found in pairs, rather than dense aggregations. Average sizes of ovigerous and non-ovigerous individuals in dense colonies of Synalpheus brooksi and S. pectiniger did not differ significantly. However, total body length of individuals differed within species groups, specifically related to sex and presence of ova. Within colonies of S. brooksi, mid-development, or ‘transitional’ individuals, were discovered in nearly all populations. However, the reproductive and social function of these individuals displaying mixed sexual characteristics could not be determined from this study. Individuals of S. brooksi displaying ‘transitional’ external morphology, i.e. masculine abdominal pleura paired with clutches of eggs, displayed higher incidences of intersex gonopores per colony than did conspecific non-ovigerous and ovigerous individuals. These results suggest that colonies of S. brooksi may be comprised of a subset of helpers, or individuals undergoing a transitional sexual development phase, similar to prior published findings of intersexed helpers among eusocial colonies (Toth and Bauer 2007). In comparison to S. brooksi colonies, nearly all colonies of S. herricki and S. cf. herricki were composed of intersex individuals. In conjunction with previous instances documented in eusocial Synalpheus paraneptunus groups, the data provide substantial evidence of intersexing at all levels of social organization in Synalpheus spp. (pair living, communal, and eusocial). These findings nonetheless provide a clearer picture of how social structure and life history influence adaptation of a particular reproductive strategy. Quantifying features of Spheciospongia vesparium populations and comparing results to neighboring hosts, such as Spongia sp., provided evidence for potential influences of host choice, and variation in growth and reproductive capacity temporally and spatially. These observations of species’ growth patterns and abundances contribute greatly to our understanding of life history of Synalpheus spp., and, furthermore, adaptation of social organization.

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第20556号 / 理博第4314号 / 新制||理||1619(附属図書館) / 京都大学大学院理学研究科生物科学専攻 / (主査)教授 古市 剛史, 教授 湯本 貴和, 教授 平井 啓久 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM

Bottlenose dolphins exhibit fission-fusion social systems in which group size and composition change fluidly throughout the day. Societies are typically sexually segregated, and the quality and patterning of individual relationships in this social species shape the social structure of a population. Female dolphins usually have a large network of associates with whom they form recurring moderate bonds, while male associations are highly variable due to their mating strategies. Males employ one of two strategies; males may be solitary, and encounter and herd females individually, while others may form strong bonds with one to two other males and cooperatively herd individual females in the shape of a first-order alliance. Second-order alliances are more uncommon and have only been observed in Shark Bay, Australia, and more recently within the St. Johns River (SJR), Jacksonville, Florida. Given the inter-population variation in male mating strategies, greater documentation of social structure in neighboring populations along the Atlantic coast is needed. Therefore, chapter one documents the social structure of the Indian River Lagoon (IRL) estuarine system where dolphins have experienced recurrent cetacean morbillivirus (CeMV) epizootics. Although environmental disturbances can affect both social and mating systems, IRL dolphin sociality does not seem to be affected by the 2008 CeMV mass mortality event. Additionally, males only form first-order alliances within this population. Because multi-level alliances are unique to the SJR in this region, chapter two analyzes the stability and function of SJR alliances. Both first- and second-order alliances exhibited variation in stability, while alliance association appears dependent on female presence. Thus, SJR alliances likely function within a reproductive context. Together, this work provides insight into the social and mating systems of bottlenose dolphins, as well as the function of multi-level alliances at a relatively new study site.