Out to sea: ocean currents and patterns of asymmetric gene flow in an intertidal fish species.

Passive dispersal via wind or ocean currents can drive asymmetric gene flow, which influences patterns of genetic variation and the capacity of populations to evolve in response to environmental change. The mangrove rivulus fish (), hereafter "rivulus," is an intertidal fish species restricted to the highly fragmented New World mangrove forests of Central America, the Caribbean, the Bahamas, and Florida. Mangrove patches are biological islands with dramatic differences in both abiotic and biotic conditions compared to adjacent habitat.

Severe inbreeding, increased mutation load and gene loss-of-function in the critically endangered Devils Hole pupfish.

Small populations with limited range are often threatened by inbreeding and reduced genetic diversity, which can reduce fitness and exacerbate population decline. One of the most extreme natural examples is the Devils Hole pupfish (), an iconic and critically endangered species with the smallest known range of any vertebrate. This species has experienced severe declines in population size over the last 30 years and suffered major bottlenecks in 2007 and 2013, when the population shrunk to 38 and 35 individuals, respectively.

Diabolical survival in Death Valley: recent pupfish colonization, gene flow and genetic assimilation in the smallest species range on earth.

One of the most endangered vertebrates, the Devils Hole pupfish Cyprinodon diabolis, survives in a nearly impossible environment: a narrow subterranean fissure in the hottest desert on earth, Death Valley. This species became a conservation icon after a landmark 1976 US Supreme Court case affirming federal groundwater rights to its unique habitat. However, one outstanding question about this species remains unresolved: how long has diabolis persisted in this hellish environment? We used next-generation sequencing of over 13 000 loci to infer the demographic history of pupfishes in Death Valley.

Genetic Subdivision and Variation in Selfing Rates Among Central American Populations of the Mangrove Rivulus, Kryptolebias marmoratus.

We used 32 polymorphic microsatellite loci to investigate how a mixed-mating system affects population genetic structure in Central American populations (N = 243 individuals) of the killifish Kryptolebias marmoratus (mangrove rivulus), 1 of 2 of the world's only known self-fertilizing vertebrates. Results were also compared with previous microsatellite surveys of Floridian populations of this species. For several populations in Belize and Honduras, population structure and genetic differentiation were pronounced and higher than in Florida, even though the opposite trend was expected because populations in the latter region were presumably smaller and highly selfing.

A novel terrestrial fish habitat inside emergent logs.

Reports of new habitats for a major group of organisms are rare. Fishes display diverse adaptations for temporary (amphibious) existence on land, but to our knowledge, none have ever been reported regularly living inside emergent logs. Here, we show that the mangrove killifish, Kryptolebias marmoratus, a species previously known to emerse (leave the water) regularly, is now known to emerse and aggregate in large numbers inside decaying mangrove logs that have been "galleried" by terrestrial insects.

Strong population structure despite evidence of recent migration in a selfing hermaphroditic vertebrate, the mangrove killifish (Kryptolebias marmoratus).

We employ a battery of 33 polymorphic microsatellite loci to describe geographical population structure of the mangrove killifish (Kryptolebias marmoratus), the only vertebrate species known to have a mixed-mating system of selfing and outcrossing. Significant population genetic structure was detected at spatial scales ranging from tens to hundreds of kilometres in Florida, Belize, and the Bahamas. The wealth of genotypic information, coupled with the highly inbred nature of most killifish lineages due to predominant selfing, also permitted treatments of individual fish as units of analysis.

A mixed-mating strategy in a hermaphroditic vertebrate.

Mixed-mating systems, in which hermaphrodites can either self-fertilize or outcross, are common in many species of plants and invertebrates and have been informative models for studying the selective forces that can maintain both inbreeding and outbreeding in populations. Here, we document a remarkable instance of evolutionary convergence to an analogous mixed mating system by a vertebrate, the mangrove killifish (Kryptolebias marmoratus). In this androdioecious species, most individuals are simultaneous hermaphrodites that characteristically self-fertilize, resulting in local populations that consist of (nearly) homozygous lines.

Extensive outcrossing and androdioecy in a vertebrate species that otherwise reproduces as a self-fertilizing hermaphrodite.

The mangrove killifish (Kryptolebias marmoratus) is the only vertebrate known to be capable of self-fertilization. Its gonad is typically an ovotestis that simultaneously produces eggs and sperm, and fertilization is internal. Although most populations of this species consist primarily or exclusively of hermaphroditic individuals, gonochoristic males occur at approximately 20% frequency in a natural population at Twin Cays, Belize.

EVIDENCE THAT AN OUTCROSSING POPULATION IS A DERIVED LINEAGE IN A HERMAPHRODITIC FISH (RIVULUS MARMORATUS).

Rivulus marmoratus is the only known vertebrate with obligate, synchronous hermaphroditic fertilization. Males can be experimentally induced in the laboratory and are rare or absent in most populations, but at the isolated Twin Cays, Belize, locality, males are relatively abundant. At this locality, evidence of outcrossing has been documented in this otherwise automictic cloning species.

EXTENSIVE CHROMOSOMAL DIVERGENCE WITHIN A SINGLE RIVER BASIN IN THE GOODEID FISH, ILYODON FURCIDENS.

Extensive variation in the number of metacentric chromosomes exists among populations of the viviparous goodeid fish, Ilyodon furcidens, in the Río Coahuayana basin of south central Mexico (states of Colima and Jalisco). The variation can be divided, somewhat arbitrarily, into four "cytotypes" with 0-2, 0-4, 6 and 10-16 metacentrics. Of these, the first, shared with the closely adjacent Río Armería and similar to other species of Ilyodon, is probably ancestral.