Cannibalism of offspring is a common yet seemingly paradoxical phenomenon observed across a wide variety of taxa. Behavioural ecologists have been particularly interested in understanding this behaviour within the context of parental care. This is because, superficially, offspring cannibalism appears counterproductive to the goals of a caring parent, which are often achieved by nurturing and protecting their young. Despite the prevalence of offspring cannibalism in many taxa, we still have a poor evolutionary understanding of this intriguing behaviour. Many hypotheses have been proposed explaining why parents may terminate and consume offspring, however, empirical tests of these hypotheses frequently return mixed results, and few examples exist in which multiple hypotheses for cannibalism have been tested using the same model study system. Over the course of my PhD thesis, I tested different cannibalism hypotheses in a novel study organism, the plainfin midshipman fish (Porichthys notatus), a species of paternal care-giving toadfish that frequently engages in offspring cannibalism. I first characterized the factors that underlie male reproductive success in this species to provide a broader understanding of their reproductive ecology and a background for the cannibalism studies in my later chapters. I showed that both male size and nest size are important correlates of male reproductive success (e.g. mate attraction, egg acquisition, and rearing success) in this system, and that morphological, physiological, and ecological variables can also have an impact on reproductive success (Chapter 2). Next, I conducted a series of field and laboratory studies to uncover the factors that select for offspring cannibalism in this species. In particular, I investigated whether offspring cannibalism serves to replenish dwindling energy reserves and/or occurs when paternity over a brood is likely to be low. I showed that although plainfin midshipman males endure a long and energetically taxing parental care period, they cannibalize offspring most frequently early in the breeding season, the time period when the males are in their best body condition but when male-male competition is also at its peak (Chapter 3). Using a direct comparison of males that had recently cannibalized offspring versus those that had not, I showed that the males with the lowest energy reserves were actually the least likely to have offspring in their digestive tracts, suggesting that offspring cannibalism is not driven by immediate energetic need (Chapter 4). I then tested whether males assess their paternity using direct or indirect offspring cues, and showed that males use the act of a nest take-over as reliable indirect cues of their paternity over a brood (Chapter 5). Altogether, my results further our understanding of the reproductive ecology of the plainfin midshipman fish, and provide a foundation upon which to assess and test between cannibalism hypotheses in this species and others. My thesis work demonstrates the advantage of studying multiple cannibalism hypotheses in a single study system, and through this approach we can gain a more accurate evolutionary understanding of how the phenomenon of offspring cannibalism is maintained in different species. / Thesis / Doctor of Philosophy (PhD)
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/22036 |
| Date | 11 1900 |
| Creators | Bose, Aneesh |
| Contributors | Balshine, Sigal, Psychology |
| Source Sets | McMaster University |
| Language | English |
| Detected Language | English |
| Type | Thesis |
Page generated in 0.0018 seconds