B.M. Titus, M. Daly, N. Hamilton, M.L. Berumen, J.A. Baeza
Journal of Biogeography, pp. 1-13, (2018)
Allopatric speciation, Coral reefs, Crustacean, Cryptic species, Gene flow, Introgression
Aim: The “sexy shrimp” Thor amboinensis is currently considered a single circumtropical
species. However, the tropical oceans are partitioned by hard and soft barriers
to dispersal, providing ample opportunity for allopatric speciation. Herein, we
test the null hypothesis that T. amboinensis is a single global species, reconstruct its
global biogeographical history, and comment on population-level patterns throughout
the Tropical Western Atlantic.
Location: Coral reefs in all tropical oceans.
Methods: Specimens of Thor amboinensis were obtained through field collection
and museum holdings. We used one mitochondrial (COI) and two nuclear (NaK, enolase)
gene fragments for global species delimitation and phylogenetic analyses
(n = 83 individuals, 30 sample localities), while phylogeographical reconstruction in
the TWA was based on COI only (n = 303 individuals, 10 sample localities).
Results: We found evidence for at least five cryptic lineages (9%–22% COI pairwise
sequence divergence): four in the Indo-West Pacific and one in the Tropical Western
Atlantic. Phylogenetic reconstruction revealed that endemic lineages from
Japan and the South Central Pacific are more closely related to the Tropical Western
Atlantic lineage than to a co-occurring lineage that is widespread throughout
the Indo-West Pacific. Concatenated and species tree phylogenetic analyses differ
in the placement of an endemic Red Sea lineage and suggest alternate dispersal
pathways into the Atlantic. Phylogeographical reconstruction throughout the Tropical
Western Atlantic reveals little genetic structure over more than 3,000 km.
Main conclusions: Thor amboinensis is a species complex that has undergone a series
of allopatric speciation events and whose members are in secondary contact in
the Indo-West Pacific. Nuclear- and mitochondrial- gene phylogenies show evidence
of introgression between lineages inferred to have been separated more than
20 Ma. Phylogenetic discordance between multi-locus analyses suggest that T.
amboinensis originated in the Tethys sea and dispersed into the Atlantic and IndoWest
Pacific through the Tethys seaway or, alternatively, originated in the Indo-West Pacific and dispersed into the Atlantic around South Africa. Population-level
patterns in the Caribbean indicate extensive gene flow across the region.