Relatedness and last male sperm precedence in Cheilomenes sexmaculata: Implications for inbreeding avoidance

Abstract

Avoidance to mate with relatives is a common evolutionary strategy, as it helps maintain genetic diversity and overall fitness within populations. Females often prefer unrelated males to mitigate the risks associated with inbreeding, such as the expression of deleterious recessive alleles. This preference can involve various post-copulatory mechanisms through which females bias paternity towards males with potentially better genes. The phenomenon of last male sperm precedence, where the last male to mate with a female tends to sire the majority of offspring, is well-documented in ladybird beetles. However, how relatedness affects this phenomenon remains unclear. This study aims to investigate whether paternity share is altered when the last male to mate with a female is related to her. By conducting double mating experiments with two different morphs (typical and intermediate) as phenotypic markers, we seek to determine if relatedness disrupts last male sperm precedence. It was hypothesised that females of Cheilomenes sexmaculata will prefer unrelated males over related ones, irrespective of mating order, potentially breaking down the last male sperm precedence. This preference for unrelated males was reflected in our results with unrelated males exhibiting enhanced reproductive success. Females were more fecund and exhibited higher egg viability with unrelated males. Greater paternity share was observed for unrelated males when the second male was related to the female. This study highlights the dynamic nature of sperm precedence and the role of mate quality in female mate choice, emphasizing the importance of inbreeding avoidance in sexual selection.