Environmental diel variation, parasite loads, and local population structuring of a mixed‐mating mangrove fish

Abstract

Genetic variation within populations depends on population size, spatial structuring, and environmental variation, but is also influenced by mating system. Mangroves are some of the most productive and threatened ecosystems on earth and harbor a large proportion of species with mixed-mating (self-fertilization and outcrossing). Understanding population structuring in mixed-mating species is critical for conserving and managing these complex ecosystems. Kryptolebias marmoratus is a unique mixed-mating vertebrate inhabiting mangrove swamps under highly variable tidal regimes and environmental conditions. We hypothesized that geographical isolation and ecological pressures influence outcrossing rates and genetic diversity, and ultimately determine the local population structuring of K. marmoratus. By comparing genetic variation at 32 microsatellites, diel fluctuations of environmental parameters, and parasite loads among four locations with different degrees of isolation, we found significant differences in genetic diversity and genotypic composition but little evidence of isolation by distance. Locations also differed in environmental diel fluctuation and parasite composition. Our results suggest that mating system, influenced by environmental instability and parasites, underpins local population structuring of K. marmoratus. More generally, we discuss how the conservation of selfing species inhabiting mangroves and other biodiversity hotspots may benefit from knowledge of mating strategies and population structuring at small spatial scales.

First record of a male of Kryptolebias hermaphroditus Costa, 2011 (Cyprinodontiformes: Cynolebiidae)

“…The other one, from Florida, USA, exhibited a bright orange coloration almost devoid of dark chromatophores, except the head. Ellison et al (2012) also found a male of K. marmoratus with orange coloration, faded ocellus and black borders on the anal and caudal fins in Belize; a pattern similar to that of the K. hermaphroditus male herein described.…”

Epigenetic regulation of sex ratios may explain natural variation in self-fertilization rates

“…Thus, males may play an important adaptive role in mixed-mating species where hermaphrodites can selffertilize but not outcross with other hermaphrodites. The environmental instability of the K. marmoratus habitat [64], widely different availability of males in different areas (less than 1% to greater than 20%) and the uniform distribution of isogenic lineages, without evidence of high local frequencies [65], suggest that reproductive assurance [66] may be the main adaptive advantage of selfing for K. marmoratus, as for other selfing species [65].…”

Maintaining functional major histocompatibility complex diversity under inbreeding: the case of a selfing vertebrate

“…of MHC supertypes). INSTRUCT was run ten times for each value of K (1 -10) with a burn-in period of 10 000 replicates followed by 50 000 replicates to collect estimated parameters and likelihoods, as detailed in Ellison et al [67]. Fully homozygous individuals were excluded from this analysis as INSTRUCT is unable to estimate the number of selfing generations under total homozygosity.…”