RESUMEN
Sperm whales have a multi-level social structure based upon long-term, cooperative social units. What role kinship plays in structuring this society is poorly understood. We combined extensive association data (518 days, during 2005-2016) and genetic data (18 microsatellites and 346 bp mitochondrial DNA (mtDNA) control region sequences) for 65 individuals from 12 social units from the Eastern Caribbean to examine patterns of kinship and social behaviour. Social units were clearly matrilineally based, evidenced by greater relatedness within social units (mean r = 0.14) than between them (mean r = 0.00) and uniform mtDNA haplotypes within social units. Additionally, most individuals (82.5%) had a first-degree relative in their social unit, while we found no first-degree relatives between social units. Generally and within social units, individuals associated more with their closer relatives (matrix correlations: 0.18-0.25). However, excepting a highly related pair of social units that merged over the study period, associations between social units were not correlated with kinship (p > 0.1). These results are the first to robustly demonstrate kinship's contribution to social unit composition and association preferences, though they also reveal variability in association preferences that is unexplained by kinship. Comparisons with other matrilineal species highlight the range of possible matrilineal societies and how they can vary between and even within species.
RESUMEN
Reproductive isolation--the key event in speciation--can evolve when sexual conflict causes selection favoring different combinations of male and female adaptations in different populations. Likely targets of such selection include genes that encode proteins on the surfaces of sperm and eggs, but no previous study has demonstrated intraspecific coevolution of interacting gamete recognition genes under selection. Here, we show that selection drives coevolution between an egg receptor for sperm (OBi1) and a sperm acrosomal protein (bindin) in diverging populations of a sea star (Patiria miniata). We found positive selection on OBi1 in an exon encoding part of its predicted substrate-binding protein domain, the ligand for which is found in bindin. Gene flow was zero for the parts of bindin and OBi1 in which selection for high rates of amino acid substitution was detected; higher gene flow for other parts of the genome indicated selection against immigrant alleles at bindin and OBi1. Populations differed in allele frequencies at two key positively selected sites (one in each gene), and differences at those sites predicted fertilization rate variation among male-female pairs. These patterns suggest adaptively evolving loci that influence reproductive isolation between populations.
