Genetic diversity and population structure of Caribbean marine invertebrates
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Abstract
Natural populations of many marine invertebrates are under pressure by fisheries due
to the increasing demand and unit prices leading to overexploitation. I examined the genetic
variation of two marine invertebrates: the corallimorpharian Ricordea florida and the emerald
crab Mithraculus sculptus both of which are heavily traded by the marine aquarium industry.
A third species studied, the commensal barnacle Chelonibia caretta, was not under direct
fishing pressure, but its host is an endangered species, the hawksbill sea turtle (Eretmochelys
imbricata). Using direct sequencing of mitochondrial genes (COI and 16S) and the nuclear
the ITS region (ITS1, 5.8S, and ITS2), the phylogeography and genetic population structure
of these invertebrates were characterized. The genetic diversity in C. caretta was low
compared to published sequences from populations of barnacles attached to fixed substrata.
However, genetic diversity values from C. caretta were comparable to those reported from C.
testudinaria, an epibiont barnacle on loggerhead turtles. Analysis of molecular variance and
phylogenetic analysis of the sampled turtle epibionts indicated that they are genetically
homogeneous, irrespective of the host or host gender. In contrast, the phylogeography of the
ITS region of the coral R. florida uncovered two partial sympatric genetic lineages. These
lineages showed two highly supported monophyletic groups when they were compared
phylogenetically against published nuclear ribosomal sequences of other genera of
Corallimorpharia (Actinodiscus, Amplexidiscus, Corynactis, and Rhodactis). Similarly to R.
florida, the phylogeographic analysis of M. sculptus based on 16S revealed two distinct
lineages distributed throughout the sampled region. The analysis of molecular variance and
the phylogeography of the sampled populations of M. sculptus reflected that most of the
specimens within each lilneage were collected from demographically open populations
within the western Caribbean. In general, the three species studied are consistent with the prediction that higher rates
of dispersal reduce population divergence and estimates of nucleotide diversity. As in
previous studies, the absence of genetic differentiation between geographical distant
populations of these species suggests high connectivity between all sampled areas.
Additionally, the presence of cryptic lineages confirms concerns regarding that biodiversity
can be vastly understudied for marine environment. Las poblaciones naturales de muchos invertebrados están bajo presión por las
pesquerías debido a su creciente demanda y valor comercial, que conducen a su sobreexplotación.
Yo examiné la variación genética de dos especies de invertebrados marinos: el
corallimorfario Ricorea florida y el cangrejo esmeralda Mithraculus sculptus, ambos
cosechados extensamente para la industria de acuarios marinos. Una tercera especie fue
estudiada, la bayoca comensalista Chelonibia caretta, la cual no está bajo presión directa de
la pesquería, pero su hospedero, el carey de concha (Eretmochelys imbricata), es una especie
de tortuga marina amenazada. Utilizando amplificaciones directas de genes mitocondriales
(COI y 16S) y nucleares (ITS1, 5.8S y ITS2) se caracterizó la filogeografía y estructura
genética poblacional de estos invertebrados. La diversidad genética de Chelonibia caretta fue
baja al compararla con secuencias publicadas de otras especies de bayocas sobre substratos
fijos. Sin embargo, los valores de la variabilidad genética para C. caretta son comparables
con aquellos publicados para C. testudinaria, bayoca epibionte de la tortuga marina
cabezona. Análisis de variación molecular y análisis filogenético de los epibiontes
muestreados de la tortuga indicaron que éstos son genéticamente homogéneos,
independientemente del hospedero o del género del hospedero. En contraste, los análisis de la
región del ITS de R. florida revelaron dos linajes genéticos parcialmente solapados. Estos
linajes fueron comparados filogenéticamente contra secuencias ribosomales nucleares
publicadas de otros géneros de Corallimorpharia (Actinodiscus, Amplexidiscus, Corynactis y
Rhodactis) y cada linaje formó un grupo monofilético altamente apoyado. Al igual que para
R. florida, los análisis filogenéticos del 16S de Mithraculus sculptus, revelaron dos linajes
distribuidos a través de la región muestreada. Los análisis de varianza molecular y la
filogeografia de las poblaciones muestreadas de M. sculptus reflejaron que la mayor parte de
los especímenes, dentro de cada linage, fueron colectados de poblaciones demográficamente abiertas dentro del Caribe occidental.
En general, las tres especies estudiadas son consistentes con la predicción de que si
los índices de dispersión son altos disminuyen la divergencia y los estimados de diversidad
de nucleótidos. Como en estudios previos, la ausencia de la diferenciación genética entre
poblaciones geográficamente distantes de estas especies sugiere una alta conectividad entre
las áreas muestreadas. En adición, la presencia de linajes crípticos confirma la preocupación
de que la biodiversidad está sub-estimada en los ambientes marinos.
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