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Evidence for rapid downward fecundity selection in an ectoparasite ( Philornis downsi ) with earlier host mortality in Darwin’s finches
Author(s) -
Common Lauren K.,
O’Connor Jody A.,
Dudaniec Rachael Y.,
Peters Katharina J.,
Kleindorfer Sonia
Publication year - 2020
Publication title -
journal of evolutionary biology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.289
H-Index - 128
eISSN - 1420-9101
pISSN - 1010-061X
DOI - 10.1111/jeb.13588
Subject(s) - fecundity , biology , zoology , host (biology) , sexual selection , natural selection , ecology , parasitism , parasite hosting , demography , population , sociology , world wide web , computer science
Fecundity selection is a critical component of fitness and a major driver of adaptive evolution. Trade‐offs between parasite mortality and host resources are likely to impose a selection pressure on parasite fecundity, but this is little studied in natural systems. The ‘fecundity advantage hypothesis’ predicts female‐biased sexual size dimorphism whereby larger females produce more offspring. Parasitic insects are useful for exploring the interplay between host resource availability and parasite fecundity, because female body size is a reliable proxy for fecundity in insects. Here we explore temporal changes in body size in the myiasis‐causing parasite Philornis downsi (Diptera: Muscidae) on the Galápagos Islands under conditions of earlier in‐nest host mortality. We aim to investigate the effects of decreasing host resources on parasite body size and fecundity. Across a 12‐year period, we observed a mean of c . 17% P. downsi mortality in host nests with 55 ± 6.2% host mortality and a trend of c . 66% higher host mortality throughout the study period. Using specimens from 116 Darwin's finch nests (Passeriformes: Thraupidae) and 114 traps, we found that over time, P. downsi pupae mass decreased by c . 32%, and male ( c . 6%) and female adult size ( c . 11%) decreased. Notably, females had c . 26% smaller abdomens in later years, and female abdomen size was correlated with number of eggs. Our findings imply natural selection for faster P. downsi pupation and consequently smaller body size and lower parasite fecundity in this newly evolving host–parasite system.