Genetic consequences of social structure in the golden-crowned sifaka

Abstract

Many species are structured in social groups (SGs) where individuals exhibit complex mating strategies. Yet, most population genetic studies ignore SGs either treating them as small random-mating units or focusing on a higher hierarchical level (the population). Empirical studies acknowledging SGs have found an overall excess of heterozygotes within SGs and usually invoke inbreeding avoidance strategies to explain this finding. However, there is a lack of null models against which ecological theories can be tested and inbreeding avoidance quantified. Here, we investigate inbreeding (deviation from random mating) in an endangered forest-dwelling pair-living lemur species (Propithecus tattersalli). In particular, we measure the inbreeding coefficient (FIS) in empirical data at different scales: SGs, sampling sites and forest patches. We observe high excess of heterozygotes within SGs. The magnitude of this excess is highly dependent on the sampling scheme: while offspring are characterised by a high excess of heterozygotes (FIS < 0), the reproductive pair does not show dramatic departures from Hardy–Weinberg expectations. Moreover, the heterozygosity excess disappears at larger geographic scales (sites and forests). We use a modelling framework that incorporates details of the sifaka mating system but does not include active inbreeding avoidance mechanisms. The simulated data show that, although apparent “random mating” or even inbreeding may occur at the “population” level, outbreeding is maintained within SGs. Altogether our results suggest that social structure leads to high levels of outbreeding without the need for active inbreeding avoidance mechanisms. Thus, demonstrating and measuring the existence of active inbreeding avoidance mechanisms may be more difficult than usually assumed.

A new set of microsatellite markers for Phoxinus lumaireul senso lato, Phoxinus marsilii and Phoxinus krkae for population and molecular taxonomic studies

“…Negative F IS coefficient in population B (Papuk Mt.) indicates the excess in the number of heterozygotes, meaning that mating occurs more often between individuals drawn at random from the (sub)population than between more closely related individuals (Parreira et al ., 2020). Distribution of the Croatian population of P. marsilii is quite narrow (<500 km 2 ), with streams at Papuk Mt.…”

Comparative genomic analysis of sifakas ( Propithecus ) reveals selection for folivory and high heterozygosity despite endangered status

“…These dynamics lead to a “neighborhood”-like intermediate level of hierarchical social organization ( 88 ). P. tattersalli and P. verreauxi social groups have been found to exhibit excess heterozygosity ( 89 , 90 ), indicating that relatively small-scale social structure can generate and maintain genetic diversity, although the relationship between heterozygosity maintained at the social group level and at a larger spatial scale, such as a metapopulation, is not straightforward ( 90 ).…”

Impact of model assumptions on demographic inferences: the case study of two sympatric mouse lemurs in northwestern Madagascar

“…Knowing that population genetics analyses can be biased by social structure and relatedness between individuals (e.g., [ 120 , 121 ]), a relatedness analyses was performed next. Relatedness between two individuals is usually described by the concept of identity-by-descent (IBD), where two alleles are considered identical by descent if they recently descended from a common ancestral allele [ 117 , 122 ].…”