Date of Award

Spring 5-2017

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Ocean Science and Technology

Committee Chair

Dr. Eric Saillant

Committee Chair Department

Ocean Science and Technology

Committee Member 2

Dr. Chet Rakocinski

Committee Member 2 Department

Ocean Science and Technology

Committee Member 3

Dr. Donald Johnson

Committee Member 4

James Franks

Abstract

The gray triggerfish (Balistes capriscus) and the queen triggerfish (Balistes vetula) are two exploited reef fish distributed in tropical and temperate shelf waters of the Atlantic Ocean and the Mediterranean Sea. Both species are highly sedentary as adults but disperse pelagic larvae for extended periods of time potentially allowing connectivity across long distances under the action of oceanic currents. In this work population structure, phylogeography, and migration patterns were examined in the two species and contrasted with predictions of larval transport based on surface circulation data. A total of 1,017 gray triggerfish from twelve sampling localities spanning the species distribution range were assayed at 17 homologous microsatellite markers and sequence variation at the ND4 mitochondrial gene. Four genetically distinct populations were detected including (i) a North Atlantic group that comprised the North American, European, and Northwest African populations, (ii) a Mediterranean group that was inferred to result from a recent colonization of the Mediterranean Sea by a small number of migrants of North Atlantic origin, (iii) a southeastern Atlantic group that included populations from the Gulf of Guinea and Southwest Africa, and (iv) a southwestern Atlantic group recently diverged from the southeastern group. Analysis of phylogeography supported long-term historical isolation of the South Atlantic and North Atlantic groups. Assignment tests and isolation-by-distance analysis supported the hypothesis of long-distance connectivity with evidence for transatlantic migrations and estimates of the mean dispersal distance of 740 km or greater. The high estimates of contemporaneous migration rates (up to 36.7%) may reflect increased larval transport in connection with the recent development of new Sargassum in the equatorial region. Analysis of high density genome scans revealed homogeneous distributions of genetic variants among queen triggerfish from the French Antilles, the U.S. Virgin-Islands, and South Florida, suggesting high connectivity is occurring across the region.

These findings suggest that, in both species, local recruitment depends largely on the output of spawning populations located hundreds or thousands of kilometers away from a given stock, highlighting the need to conserve populations across each species’ range in particular in areas where circulation patterns predict a low likelihood of incoming migrants.

ORCID ID

orcid.org/0000-0001-6902-1721

Available for download on Sunday, May 12, 2019

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