Abstract: 1. Coastal organisms are predicted to be particularly susceptible to the impact of global warming. In this study the distribution and relative abundance of two coastal invertebrates, Coelopa frigida (Fabricius) and C. pilipes are investigated. 2. Coelopa pilipes has a more southerly distribution than C. frigida, and prefers a warmer climate. Coelopa pilipes is less resistant to sub-zero temperatures than C. frigida and its northerly distribution is probably limited by cold winter days. 3. The most recent distribution map of C. frigida and C. pilipes in northern Europe was published a decade ago and showed the northerly extent of the distribution of C. pilipes reaching the north coast of mainland Scotland but its complete absence from the Western and Northern Isles. 4. C. pilipes has now spread throughout the Western Isles and the Orkney Islands but is still absent from Shetland. There has also been an increase in the relative frequency of C. pilipes at sites harbouring coelopids on the British mainland. A similar pattern of distribution change along the west coast of Sweden is reported. 5. It is proposed that these changes have occurred primarily as a result of global warming and in particular due to the recent increase in winter temperatures. A number of other indirect effects may have also contributed to these changes, including a probable change in macroalgae distribution. The implications of these changes for the wrack bed ecosystem and at higher trophic levels are considered.
Abstract: The seaweed fly, Coelopa frigida, exhibits LMSP. A large chromosomal inversion system affects many traits including egg-to-adult viability via heterosis. Consequently, there is also considerable potential for cryptic female mate choice to operate on the basis of sperm karyotype. Here, we investigated the effect of time interval and chromosomal inversion karyotype on postcopulatory sexual selection. Homokaryotypic females were mated with a male of the same and a male of the opposite homokaryotype. The order of the matings was varied so cryptic female mate choice could operate either in concert or antagonistically with LMSP. LMSP was found when there was a 24 h time interval between matings, irrespective of the order in which the males were mated. However, when the males were mated in quick succession the order of mating was important. When LMSP and cryptic female mate choice work in concert a high level of LMSP was found. However, when the male of opposite homokaryotype mated first, then first male sperm precedence was observed. This suggests that polyandrous females might be able to bias paternity but only when matings occur in quick succession. Consequently, population density is likely to affect the operation of postcopulatory sexual selection.
Abstract: This thesis describes a collection of experiments investigating sexual conflict and cryptic female choice in the Coelopidae. An experiment examining the effect of inversion karyotype in C. frigida revealed that male karyotype has no direct influence on male willingness to mate or other mating interactions, however, male size and karyotype have an influence over the female rejection response. There appears to be no clear genetic effect of female karyotype on female rejection behaviour, which leaves the question as to why females are mated with more often, unanswered. The extent to which convenience polyandry occurs in C. frigida was also examined through the measurement of female re-mating frequency in wild populations. Females were found to mate hundreds of times in their lifetimes, making C. frigida an extremely promiscuous species with great potential for post-copulatory sexual selection to occur in this species. Evidence was found for cryptic female choice as females may have the ability to select sperm from within the ejaculate of a single heterokaryotypic male to produce fitter heterokaryotypic offspring. Time interval between copulations and the order of polyandrous copulations with males of different chromosomal karyotypes were found to interact in their effects on P2 values. The mating systems of 5 Australasian coelopids were examined and a comparative analysis of sexually antagonistic co-evolution in 13 coelopids was carried out. Female-mediated sexual conflict appears to have played a role in increasing male size and variation in male size, though large male reluctance to mate may mask evidence for antagonistic co-evolution. ISSRs were found to be a very useful tool in determining genetic variation in C. frigida and the possible future use of this technique in paternity analysis is discussed.
