RESUMO
BACKGROUND: The formation of the Isthmus of Panama and final closure of the Central American Seaway (CAS) provides an independent calibration point for examining the rate of DNA substitutions. This vicariant event has been widely used to estimate the substitution rate across mitochondrial genomes and to date evolutionary events in other taxonomic groups. Nuclear sequence data is increasingly being used to complement mitochondrial datasets for phylogenetic and evolutionary investigations; these studies would benefit from information regarding the rate and pattern of DNA substitutions derived from the nuclear genome. RESULTS: To estimate the genome-wide neutral mutation rate (µ), genotype-by-sequencing (GBS) datasets were generated for three transisthmian species pairs in Alpheus snapping shrimp. A range of bioinformatic filtering parameters were evaluated in order to minimize potential bias in mutation rate estimates that may result from SNP filtering. Using a Bayesian coalescent approach (G-PhoCS) applied to 44,960 GBS loci, we estimated µ to be 2.64E-9 substitutions/site/year, when calibrated with the closure of the CAS at 3 Ma. Post-divergence gene flow was detected in one species pair. Failure to account for this post-split migration inflates our substitution rate estimates, emphasizing the importance of demographic methods that can accommodate gene flow. CONCLUSIONS: Results from our study, both parameter estimates and bioinformatic explorations, have broad-ranging implications for phylogeographic studies in other non-model taxa using reduced representation datasets. Our best estimate of µ that accounts for coalescent and demographic processes is remarkably similar to experimentally derived mutation rates in model arthropod systems. These results contradicted recent suggestions that the closure of the Isthmus was completed much earlier (around 10 Ma), as mutation rates based on an early calibration resulted in uncharacteristically low genomic mutation rates. Also, stricter filtering parameters resulted in biased datasets that generated lower mutation rate estimates and influenced demographic parameters, serving as a cautionary tale for the adherence to conservative bioinformatic strategies when generating reduced-representation datasets at the species level. To our knowledge this is the first use of transisthmian species pairs to calibrate the rate of molecular evolution from GBS data.
Assuntos
Decápodes , Taxa de Mutação , Animais , Teorema de Bayes , Decápodes/genética , Panamá , FilogeniaRESUMO
Alpheus viserion sp. n. is described based on the material from Bocas del Toro archipelago on the Caribbean coast of Panama. The new species is morphologically closest to three members of the speciose A. armillatus H. Milne-Edwards, 1837 species complex, viz. A. carlae Anker, 2012, A. angulosus McClure, 2002, and A. tenuis Kim Abele, 1988, differing from them, as well as from all the other species currently included in this complex, by a suite of morphological characters and a diagnostic colour pattern. With the description of yet another new shrimp species from Bocas del Toro, the authors hope to contribute to the awareness that this archipelago represents one of the most biologically diverse places in the Caribbean Sea and to encourage the preservation of the remaining natural habitats of this unique area.
Assuntos
Decápodes , Distribuição Animal , Estruturas Animais , Animais , Região do Caribe , PanamáRESUMO
The status of the common intertidal snapping shrimp, Alpheus inopinatus Holthuis Gottlieb, 1958, is discussed based on newly collected material from Kuwait. Alpheus inopinatus was previously confused with morphologically very similar species in the Alpheus lobidens De Haan, 1849 species complex, formerly identified as A. crassimanus Heller, 1862 and herein tentatively referred to as A. cf. lobidens. The material herein examined strongly supports the validity of A. inopinatus based on several morphological characters, as well as differences in the colour pattern, compared to other members of the A. lobidens complex.
Assuntos
Decápodes , Distribuição Animal , Estruturas Animais , Animais , KuweitRESUMO
A new snapping shrimp, Alpheus perlas sp. nov., is described based on a single complete male specimen collected on a shallow mudflat at Casayeta Island in the Las Perlas Archipelago, Gulf of Panama. The new species belongs to the large A. edwardsii (Audouin, 1821) species group characterised essentially by the presence of two notches on the major chela palm, with the dorsal notch extending posteriorly on the mesial surface. Within the eastern Pacific members of the A. edwardsii group, A. perlas sp. nov. appears to be morphologically closest to A. latus Kim Abele, 1988 and A. burukovskyi Anker Pachelle, 2015. Alpheus perlas sp. nov. does not seem to be specially adapted for digging and may be inquiline of a larger burrowing host, which currently remains unknown.
Assuntos
Decápodes , Distribuição Animal , Estruturas Animais , Animais , Ilhas , Masculino , PanamáRESUMO
Alpheus leptochiroides De Man, 1909, a poorly-known species originally described from the Kai Islands in eastern Indonesia, is reported from Kavieng, eastern Papua New Guinea, representing only the second record of this snapping shrimp and slightly extending its distribution range into the tropical western Pacific. The original description was based on a relatively young specimen, whereas the Kavieng specimen is clearly an adult male. Most importantly, several rather important characters of the species were omitted and/or not illustrated by De Man, including the unique and diagnostic rounded cuticular expansions on several areas of the third maxilliped, not present in any other alpheid shrimp. Therefore, a full redescription of the species is provided, with new detailed illustrations.
Assuntos
Decápodes , Distribuição Animal , Estruturas Animais , Animais , Masculino , ÁguaRESUMO
A new species of deep water alpheid shrimp, Alpheus luiszapatai sp. nov., from Arusí, Chocó, Pacific coast of Colombia is described. The single female known was collected between the discarded bycatch of deep water shrimp trawls dedicated to the commercial fisheries of the "coliflor" shrimp Solenocera spp. This new species is placed putatively in the Alpheus brevirostris (Olivier, 1811) species group, and share some external morphological characters with Alpheus hephaestus Bracken-Grissom Felder, 2014. It can be differentiated by the shape and ornamentation of major and minor chelipeds, the propodi and dactyli of third to fifth pereopods, the diaresis of uropodal exopod, the length of the rostral carina, color in life and bathymetric distribution. Additional comparison with another congeners pertaining to this species group complex from the eastern Pacific, western Atlantic and other oceanographic regions is discussed. A key for Alpheus brevirostris species group from the eastern Pacific is presented.
Assuntos
Decápodes , Distribuição Animal , Estruturas Animais , Animais , Tamanho Corporal , Colômbia , Feminino , ÁguaRESUMO
Divergent natural selection driven by competition for limited resources can promote speciation, even in the presence of gene flow. Reproductive isolation is more likely to result from divergent selection when the partitioned resource is closely linked to mating. Obligate symbiosis and host fidelity (mating on or near the host) can provide this link, creating ideal conditions for speciation in the absence of physical barriers to dispersal. Symbiotic organisms often experience competition for hosts, and host fidelity ensures that divergent selection for a specific host or host habitat can lead to speciation and strengthen pre-existing reproductive barriers. Here, we present evidence that diversification of a sympatric species complex occurred despite the potential for gene flow and that partitioning of host resources (both by species and by host habitat) has contributed to this diversification. Four species of snapping shrimps (Alpheus armatus, A. immaculatus, A. polystictus and A. roquensis) are distributed mainly sympatrically in the Caribbean, while the fifth species (A. rudolphi) is restricted to Brazil. All five species are obligate commensals of sea anemones with a high degree of fidelity and ecological specificity for host species and habitat. We analysed sequence data from 10 nuclear genes and the mitochondrial COI gene in 11-16 individuals from each of the Caribbean taxa and from the only available specimen of the Brazilian taxon. Phylogenetic analyses support morphology-based species assignments and a well-supported Caribbean clade. The Brazilian A. rudolphi is recovered as an outgroup to the Caribbean taxa. Isolation-migration coalescent analysis provides evidence for historical gene flow among sympatric sister species. Our data suggest that both selection for a novel host and selection for host microhabitat may have promoted diversification of this complex despite gene flow.
Assuntos
Decápodes/classificação , Fluxo Gênico , Especiação Genética , Filogenia , Anêmonas-do-Mar , Animais , Brasil , Região do Caribe , Núcleo Celular/genética , DNA Mitocondrial/genética , Decápodes/genética , Ecossistema , Modelos Genéticos , Dados de Sequência Molecular , Tipagem de Sequências Multilocus , Isolamento Reprodutivo , Seleção Genética , Especificidade da Espécie , SimpatriaRESUMO
Alpheus cedricisp. n. is described based on two specimens collected under rocks while scuba diving off the coast of Ascension Island, central Atlantic Ocean. The new species belongs to the Alpheus macrocheles (Hailstone, 1835) species complex and appears to be most closely related to the eastern-central Atlantic Alpheus macrocheles, the western Atlantic Alpheus amblyonyx Chace, 1972, and the eastern Pacific Alpheus bellimanus Lockington, 1877 and Alpheus rectus Kim & Abele, 1988. However, it differs from all these species by a combination of morphological characters and by a diagnostic and striking colour pattern.