Full thesis document accompanied by all data files and R scripts to reproduce analyses in both data chapters (2 & 3). / Animals should favour breeding locations that maximize their lifetime reproductive output. Parents ought to rear young in sites that positively affect offspring but sometimes these same sites inflict costs on parents. How parents balance their own needs against those of their offspring when selecting a site for reproduction remains unclear, particularly in animals that provide extended parental care at one location. Further, few studies have linked variation in life history traits to reproductive site choices within a single species. In this thesis, I addressed both knowledge gaps by studying the plainfin midshipman (Porichthys notatus), a marine toadfish where fathers provide sole parental care to broods of young in intertidal and shallow subtidal nests for up to two months. In Chapter 2, I measured the costs incurred by caring males and the benefits conferred to offspring in nest sites along a tidal gradient. Males suffered similar rates of body condition deterioration in all nests across the intertidal gradient. Young developed more quickly in intertidal nests compared to subtidal nests, but broods in the highest intertidal nests suffered the highest mortality rates, despite receiving more parental care from the males at these nest sites. We found the most competitive males in lower intertidal nests, a trend that agrees with life history theory—in species with relatively slow offspring development, parents should accrue greater reproductive benefits from nest sites where offspring benefits are highest. In Chapter 3, I describe a laboratory experiment designed to examine how warm water and air exposure (two abiotic conditions that vary dramatically within the intertidal) affect development and survival of plainfin midshipman young, and how these effects vary with maternal traits. Exposure to warm water enhanced embryonic and larval development rates; this effect was attenuated by air exposure. Juveniles raised in warm water also exhibited superior swimming performance, while air-exposed young suffered higher mortality rates. Although larger juveniles emerged from larger eggs, development rates were similar across egg sizes. Offspring survival increased with maternal body condition in cold water but decreased with maternal body condition in warm water. Juvenile body sizes increased with maternal condition in cold water without emersion, and in warm water with emersion—the two ecologically relevant rearing environments. Thus, low condition mothers might accrue greater benefits by depositing their eggs in nests at higher tidal elevations—where development is more rapid—further supporting the idea that among-individual variation in the expression of life history traits might influence nest site preferences in these fish. In sum, my research (Chapters 2 & 3) elucidates the link between life history traits and the spatial component of animal reproductive strategies. / Thesis / Master of Science (MSc)

Sperm competition is a widely-recognized and powerful selective force. Male accessory glands are organs found across animal taxa that can influence sperm performance, and thus may be selected for in competitive contexts. In fishes, these organs are in fact rare, but display great diversity in form and function across species. Although the accessory gland is known to play a role in mate attraction, parental care, fertilization, or post-copulatory competition in a few select species, the role of this organ remains a mystery in most species. Many fishes with accessory glands also exhibit alternative reproductive tactics (ARTs), which add an extra layer of complexity to how species respond to sperm competition. Because males of different ARTs typically experience different levels of sperm competition risk, it’s possible they may differentially invest in accessory glands to overcome this competition. In this thesis, I used the plainfin midshipman fish (Porichthys notatus), a species with both ARTs and an accessory gland, to experimentally investigate the role of the accessory gland in sperm competition and uncover how this organ may differ between ARTs. Over a two-year period, I studied tactic-specific investment in the accessory gland in fish from the beaches of British Columbia. I also examined the effects of seminal fluid, produced in part by the accessory gland, on sperm performance and morphology. I found that males adopting the ‘guarder’ male tactic invested more in one region (the lobules) of this organ, while males adopting the smaller ‘sneaker’ male tactic invested more the other region of the gland (the nodes). Using data collected over five years, I found that guarder males also invested more in their whole accessory glands. Additionally, I report that sperm swam faster in the presence of seminal fluid, and seminal fluid increased sperm head size in both male tactics and increased midpiece size in guarder males. These results suggest that the plainfin midshipman accessory gland may have dual functions, one of which may be to aid sperm competitive ability through enhancements in swimming speed and potentially more successful sperm morphology. Taken together, the results of my thesis improve our knowledge of the role of non-sperm components like seminal fluid and the accessory gland in sperm competition, and demonstrate how species with ARTs can have varying physiological responses to such competition. Only a handful of studies have considered the effects of seminal fluid on sperm performance. By examining sperm competition in a more biologically relevant way and incorporating the effects of a little-studied organ that impacts sperm competition, we should be able to more generally and accurately appreciate the dynamics of post-copulatory competition and fertilization. / Thesis / Master of Science (MSc)