Gene flow and population structure in the Mexican blind cavefish complex (Astyanax mexicanus)

Bradić, Martina; Beerli, Peter; León, Francisco J. Garcı́a de; Esquivel-Bobadilla, Sarai; Borowsky, Richard

doi:10.1186/1471-2148-12-9

Cited by 169 publications

(309 citation statements)

References 47 publications

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“…S1). This level of sequence similarity between different cave populations seems unusual, as it has been proposed that animals from the El Abra cluster of caves have arisen from independent invasions of the underground environment, though this is a topic of some debate 12,14,37 . The differences between cave and surface fish sequences, however, may simply represent more recent changes to the surface genome from the original river ancestor, rather than cave-specific evolutionary changes.…”

Section: Resultsmentioning

confidence: 99%

“…Astyanax mexicanus has established itself as an important evolutionary model system for the study of a wide variety of biological processes, not least because direct descendants of the ancestral surface dwelling form coexist with multiple isolated cave forms 14,15 . This allows direct molecular and physiological comparisons to be made between surface and cave individuals of the same species, and statements to be made about how these processes have changed after hundreds of thousands of years in complete darkness.…”

Section: Discussionmentioning

confidence: 99%

“…These changes include the loss of functional eyes and pigmentation, two regressive traits that are common to most cave species [10][11][12][13] . Astyanax has several major advantages for such studies, not least the fact that direct descendants of ancestral surface fish persist within the neighbouring rivers of the Sierra de El Abra region of North East Mexico 14,15 . This makes it possible to determine how a given biological process has evolved in constant darkness, even down to specific molecular changes, by comparing directly descendants of the founding river fish with isolated cave populations.…”

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confidence: 99%

“…This makes it possible to determine how a given biological process has evolved in constant darkness, even down to specific molecular changes, by comparing directly descendants of the founding river fish with isolated cave populations. In addition, there are numerous distinct and welldefined cave strains of Astyanax in this region of Mexico, making it possible to compare the evolution of specific traits amongst several independent populations [14][15][16][17] . As such, Astyanax mexicanus provides a unique opportunity to explore how the circadian clock has changed between river and cave following several hundred thousand years or more of constant darkness.…”

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confidence: 99%

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Circadian rhythms in Mexican blind cavefish Astyanax mexicanus in the lab and in the field

et al. 2013

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Biological clocks have evolved as an adaptation to life on a rhythmic planet, synchronising physiological processes to the environmental light-dark cycle. Here we examine circadian clock function in Mexican blind cavefish Astyanax mexicanus and its surface counterpart. In the lab, adult surface fish show robust circadian rhythms in per1, which are retained in cave populations, but with substantial alterations. These changes may be due to increased levels of light-inducible genes in cavefish, including clock repressor per2. From a molecular standpoint, cavefish appear as if they experience 'constant light' rather than perpetual darkness. Micos River samples show similar per1 oscillations to those in the lab. However, data from Chica Cave shows complete repression of clock function, while expression of several lightresponsive genes is raised, including DNA repair genes. We propose that altered expression of light-inducible genes provides a selective advantage to cavefish at the expense of a damped circadian oscillator.

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Section: Resultsmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

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Circadian rhythms in Mexican blind cavefish Astyanax mexicanus in the lab and in the field

et al. 2013

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“…This complete isolation is because of the disappearance of surface populations, unlike some other species that maintain some level of gene flow with surface-dwelling populations (Li and He, 2009;Kruckenhauser et al, 2011). The extent to which gene flow occurs between surface-and cave-dwelling forms is still debated for A. mexicanus, the model species in cavefish evolution (Bradic et al, 2012;Gross, 2012;Strecker et al, 2012). Another key factor that determines the extent of regression is time.…”

Section: Introductionmentioning

confidence: 99%

Relaxed selective constraints drove functional modifications in peripheral photoreception of the cavefish P. andruzzii and provide insight into the time of cave colonization

et al. 2016

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The genetic basis of phenotypic changes in extreme environments is a key but rather unexplored topic in animal evolution. Here we provide an exemplar case of evolution by relaxed selection in the Somalian cavefish Phreatichthys andruzzii that has evolved in the complete absence of light for at least 2.8 million years. This has resulted in extreme degenerative phenotypes, including complete eye loss and partial degeneration of the circadian clock. We have investigated the molecular evolution of the nonvisual photoreceptor melanopsin opn4m2, whose mutation contributes to the inability of peripheral clocks to respond to light. Our intra-and inter-species analyses suggest that the 'blind' clock in P. andruzzii evolved because of the loss of selective constraints on a trait that was no longer adaptive. Based on this change in selective regime, we estimate that the functional constraint on cavefish opn4m2 was relaxed at ∼ 5.3 Myr. This implies a long subterranean history, about half in complete isolation from the surface. The visual photoreceptor rhodopsin, expressed in the brain and implicated in photophobic behavior, shows similar evolutionary patterns, suggesting that extreme isolation in darkness led to a general weakening of evolutionary constraints on light-responsive mechanisms. Conversely, the same genes are still conserved in Garra barreimiae, a cavefish from Oman, that independently and more recently colonized subterranean waters and evolved troglomorphic traits. Our results contribute substantially to the open debate on the genetic bases of regressive evolution.

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The rise of Astyanax cavefish

Gross

Meyer

Perkins

2015

Developmental Dynamics

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Numerous animals have invaded subterranean caverns and evolved remarkably similar features. These features include loss of vision and pigmentation, and gains in non-visual sensation. This broad convergence echoes smaller-scale convergence, in which members of the same species repeatedly evolve the same cave-associated phenotypes. The blind Mexican tetra of the Sierra de El Abra region of northeastern Mexico has a complex origin, having recurrently colonized subterranean environments through numerous invasions of surface-dwelling fish. These colonizations likely occurred ~1–5 MYa. Despite evidence of historical and contemporary gene flow between cave and surface forms, the cave-associated phenotype appears to remain quite stable in nature. This model system has provided insight to the mechanisms of phenotypic regression, the genetic basis for constructive trait evolution, and the origin of behavioral novelties. Here, we document the rise of this model system from its discovery by a Mexican surveyor in 1936, to a powerful system for cave biology and contemporary genetic research. The recently sequenced genome provides exciting opportunities for future research, and will help resolve several long-standing biological problems.

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Gene flow and population structure in the Mexican blind cavefish complex (Astyanax mexicanus)

Cited by 169 publications

References 47 publications

Circadian rhythms in Mexican blind cavefish Astyanax mexicanus in the lab and in the field

Circadian rhythms in Mexican blind cavefish Astyanax mexicanus in the lab and in the field

Relaxed selective constraints drove functional modifications in peripheral photoreception of the cavefish P. andruzzii and provide insight into the time of cave colonization

The rise of Astyanax cavefish

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