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Human disturbance causes the formation of a hybrid swarm between two naturally sympatric fish species
Author(s) -
Hasselman Daniel J.,
Argo Emily E.,
McBride Meghan C.,
Bentzen Paul,
Schultz Thomas F.,
PerezUmphrey Anna A.,
Palkovacs Eric P.
Publication year - 2014
Publication title -
molecular ecology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.619
H-Index - 225
eISSN - 1365-294X
pISSN - 0962-1083
DOI - 10.1111/mec.12674
Subject(s) - introgression , biology , reproductive isolation , sympatric speciation , sympatry , alewife , allopatric speciation , hybrid , ecology , fish migration , animal ecology , habitat , zoology , population , genetics , predation , demography , botany , sociology , gene
Most evidence for hybrid swarm formation stemming from anthropogenic habitat disturbance comes from the breakdown of reproductive isolation between incipient species, or introgression between allopatric species following secondary contact. Human impacts on hybridization between divergent species that naturally occur in sympatry have received considerably less attention. Theory predicts that reinforcement should act to preserve reproductive isolation under such circumstances, potentially making reproductive barriers resistant to human habitat alteration. Using 15 microsatellites, we examined hybridization between sympatric populations of alewife ( Alosa pseudoharengus ) and blueback herring ( A. aestivalis ) to test whether the frequency of hybridization and pattern of introgression have been impacted by the construction of a dam that isolated formerly anadromous populations of both species in a landlocked freshwater reservoir. The frequency of hybridization and pattern of introgression differed markedly between anadromous and landlocked populations. The rangewide frequency of hybridization among anadromous populations was generally 0–8%, whereas all landlocked individuals were hybrids. Although neutral introgression was observed among anadromous hybrids, directional introgression leading to increased prevalence of alewife genotypes was detected among landlocked hybrids. We demonstrate that habitat alteration can lead to hybrid swarm formation between divergent species that naturally occur sympatrically, and provide empirical evidence that reinforcement does not always sustain reproductive isolation under such circumstances.