Reproductive Success and Factors Affecting Sexual Selection in a Fiddler Crab, Uca Mjoebergi PDF Download

Author: Huon Lyndon Clark
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Languages : en
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Book Description
Producing offspring is the most important aspect of an animal's life. Reproductive success is the cornerstone of evolution, but successful mating is a complex process that we are only starting to understand. This thesis examines five aspects of reproductive success in a fiddler crab, Uca mjoebergi. This is an ideal study species since the crabs are tractable, abundant and amenable to manipulation. In the first chapter, I examine the natural mate-searching behaviour of females and show, for the first time in any species, that there is a mosaic of preferences: females prefer males of different sizes depending on where they are in the tidal zone, and when they are mate-searching in the tidal cycle. This level of complexity in female preferences can partly explain the 'lek paradox'. In the second chapter, I examine assortative mating and show that there is a strong correlation between the size of males and females in mated pairs. I show that neither mate availability nor mating constraints can explain the pattern. Since both males and females preferentially mate with larger partners, sexual selection explains the high level of size-assortative mating. In chapter three, I revisit earlier work on this species showing that claw loss and subsequent regeneration strongly disadvantages males in terms of reproductive success. By substantially increasing the sample size, I show that males with regenerated claws are not at a mating disadvantage. This study highlights the importance of large sample sizes in behavioural studies. In chapter four, I examine the effect of temperature on mating success. Males can live in the sun or shade. There are advantages to living in the shade: males can be active for longer periods and they are less likely to dehydrate or overheat. Females that chose to mate with males living in the shade, however, would incubate their eggs at approximately 3°C lower than females incubating in sunny territories. I show that this difference in temperature does not affect the timing of crucial reproductive events and does not prevent the females from releasing their fully-formed larvae at the optimal time. In chapter five, I examine the potential consequence of habitat loss and subsequent overlap between species distributions. We can already observe this: a larger, lower-living fiddler crab is invading the habitat of Uca mjoebergi, increasing the competition between these species. I show that the disadvantages experienced by male U. mjoebergi from having a heterospecific neighbour is not necessarily as severe as common sense may suggest.