The effects of mating systems on parental care and male and female gametic investment in dunnocks

Abstract

My thesis had the following aims. First, I quantified variation and maintenance of immune-associated toll-like receptor genes between an ancestral population of dunnocks from England and an introduced population of dunnocks to New Zealand (ca. 150 years ago). Then, I used individual-level data (seven years of continuous monitoring) from the introduced population to New Zealand to achieve the followings. Second, I evaluated the effects that the two main dunnock mating systems (monogamy and polyandry) have on parental feeding allocation. Third, I assessed whether male dunnock social statuses (monogamous males, alpha polyandrous males, and beta polyandrous males) influence sperm investment. Fourth, I empirically tested five hypotheses that explain variation in egg colour and egg size, to separately quantify the roles of these two egg traits. My results are as follow. First, I found a high TLR diversity in both dunnock populations (Dunedin and Cambridge). I also found that the introduced population was slightly less diverse than the ancestral population from Cambridge. The small TLR genetic differentiation between populations did not allow me to detect strong signals of natural selection. Further, I reached a relatively similar conclusion via meta-analysis: a limited capacity of TLRs to detect signals of selection, particularly in the short timescales. Interestingly, the meta-analysis showed that high heterogeneity stemmed from between-species variation over the short timescales. This finding implies that likely genetic drift plays a role shaping TLR variation. Second, I found that females in both mating systems (monogamy and polyandry) more often fed nestlings in good condition, and less often fed nestlings in bad condition. Likewise, polyandrous males more often fed nestlings in good condition. However, monogamous males did not follow this pattern and fed all the nestlings in a more egalitarian manner. A possibility that can explain this variation in the feeding preferences between monogamous and polyandrous males is based on the uncertainty over paternity. Third, I found that the levels of the sperm competition determined sperm velocity across the three social statuses. It is, I observed that beta polyandrous males produced the fastest swimming sperm, alpha polyandrous males produced intermediate swimming sperm, and alpha monogamous males produced the slowest swimming sperm. Fourth, I found that female variation in egg size arose between years (i.e. between breeding seasons), but also that small adjustment in egg volume are possible (i.e. supporting the load-lightening hypothesis). Variation in egg colour, on the other hand, also occurred within breeding seasons.