Patricia Pérez-Barros

Pelagic swarms and beach strandings of the squat lobster Munida gregaria (Anomura: Munididae) in the Beagle Channel, Tierra del Fuego

The present article is the first formal record of pelagic swarms and beach strandings of the squat lobster Munida gregaria in the Beagle Channel, southern South America. To describe size composition and natural diet of beach strandings and swarms, samples from strandings were taken in April 2007, March 2008 and March 2010. Samples from swarms were taken in May 2007 and April 2010. Also, during November 2008 and January 2009, two acoustic surveys were carried out to describe both, horizontal distribution and school metrics of swarms. Pelagic swarms and beach strandings were composed of 100% individuals of the morph gregaria of M. gregaria. Mean size of males and females in both, beach strandings and swarms, were similar. The diet of pelagic M. gregaria was composed mainly of crustaceans, unicellular algae and small macroalgae, sediment and particulate organic matter. Swarms of pelagic Munida took the shape of extended layers of varying density and height. Their positions in the water column were also variable: swarms were found at different depths, from the subsurface layer to near the sea bottom. Occasionally, some large swarms occupied most of the water column. In the Beagle Channel, SW winds during spring tides could be a forcing factor for M. gregaria strandings. The absence of shoaling animals in the Beagle Channel between 1997 and 2002 and the recent occurrence of swarms are coincident with their appearance in other locations in Patagonia. In consequence, we hypothesize that the factor influencing the formation of swarms must be acting at a regional scale.

Absence of a prezygotic behavioural barrier to gene flow between the two sympatric morphs of the squat lobster Munida gregaria (Fabricius, 1793) (Decapoda: Anomura: Galatheidae)

Munida gregaria and M. subrugosa have been considered two different species for more than a century; however, after a recent molecular phylogenetic study, they are considered a single polymorphic species. Yet, the use of markers to diagnose species may be misleading when divergence between species is recent, since a speciation event may be obscured by the retention and stochastic sorting of ancestral polymorphisms. The morphs gregaria and subrugosa of Munida gregaria constitute an interesting case for the study of behavioural isolation since they are sympatric, breed at the same time of the year, and might have experienced a recent speciation. Mating behaviour observations and mate choice mating trials were conducted in order to investigate the potential existence of a behavioural prezygotic barrier to gene flow between these two morphs. Since factors involved in mate choice in galatheids are unknown, the four possible combinations of the two different morphs in trios were used to test for the existence of mate choice. Video recordings of all the possible trio combinations revealed that there was cross-attraction between males and females of different morphs. Females bearing partial broods participated in encounters as well as non-ovigerous females. The frequency and duration of homo- and heterotypic encounters were registered, and a reproductive isolation index was calculated for each variable for each trio. The isolation indexes calculated were not different from zero indicating random mating, and were not affected by the composition of the trio or the partial ovigerous condition of females. These results provided evidence of the absence of behavioural prezygotic barriers to gene flow between the morphs gregaria and subrugosa of M. gregaria.

Similar feeding habits of two morphs of Munida gregaria (Decapoda) evidence the lack of trophic polymorphism

Resumen en: Munida gregaria and M. subrugosa were originally described as two different species on the basis of several morphological characters, but recent studies ...

Is Munida gregaria (Crustacea: Decapoda: Munididae) a truly transpacific species?

The “East Pacific Barrier” has been recognized as the World’s largest marine biogeographic barrier. Munida gregaria is the only species of its family with transpacific populations; however, it still remains to be elucidated whether these two distantly located populations belong to the same species. In this study, we investigated the genetic cohesion of M. gregaria across the East Pacific Barrier by analyzing mitochondrial markers. Cytochrome oxidase subunit I and NADH dehydrogenase subunit 1 genes were sequenced for individuals from different areas, i.e., the southeast Pacific, the southern tip of South America, the southwest Atlantic, and the southwest Pacific. A median-joining network, pairwise FSTs, genetic diversity statistics, and neutrality tests were computed. Our results, i.e., the absence of different haplogroups on both sides of the East Pacific Barrier and existence of shared haplotypes, showed that populations on both sides of this barrier belong to the same species. At a population genetic level, our results suggest that individuals from both regions have been connected, since although some differentiation was found between the southern tip of South America and the southwest Pacific, the southeast Pacific and southwest Atlantic showed no signs of differentiation from the southwest Pacific. In addition, our results provided evidence of a population expansion in southern South America during the Pleistocene. The role of Pleistocene glaciations and the Antarctic Circumpolar Current in shaping the distribution of sub-Antarctic marine invertebrates is discussed.

Gregaria to "Subrugosa," that is the question: Shape changes under laboratory conditions in the pelagic morphotype of the squat lobster Munida gregaria (Fabricius, 1793) (Decapoda: Anomura: Munididae)

Fil: Diez, Mariano Javier. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Austral de Investigaciones Cientificas; Argentina

Incongruence between molecular and morphological characters in the southern king crabs Lithodes santolla and Lithodes confundens (Decapoda: Anomura)

The use of genetic tools has a relevant role in fishery resource management and conservation, for example, when used in species delimitation. Morphological variation can occur as an adaptative or plastic response to environmental variation, and therefore, be mistakenly used as a criterion to delimit species. Particularly, Lithodes santolla and Lihodes confundens, two commercially important lithodid species from sub-Antarctic South America, are mainly differentiated by the number and size of spines on the carapace and pereiopods. However, variability in the size of spines of L. santolla has been reported. We evaluated whether these two morphospecies constitute reciprocally monophyletic clades at the molecular level using mitochondrial markers, and performed a detailed morphological analysis of the carapace to search for correspondence between genetic and morphological differences. The Bayesian phylogenetic reconstruction showed that L. santolla and L. confundens belong to two sister clades. However, individuals identified as L. santolla and L. confundens did not resolve as reciprocally monophyletic groups. Instead, one clade was formed by individuals belonging to both morphospecies and was widely distributed, while the other one was exclusively formed by L. santolla, and its members were only found near Puerto Montt and in the Beagle Channel. No morphological characters were found on the carapace that could differentiate individuals belonging to each genetic clade. Either if the two genetic clades constitute species or remnants of two species that are merging through introgression, they represent two evolutionary significant lineages, and measures should be taken to preserve both. Our study suggests the need to revise the use of the number of spines as a relevant taxonomic character in the taxonomy of Lithodes, and to implement molecular genetic methods to control fisheries.

Relationship between energy allocation and gametogenesis in Aulacomya atra (Bivalvia: Mytilidae) in a sub-Antarctic environment

Resumen es: Se analizo la gametogenesis y la variacion temporal en la asignacion de energia a diferentes organos de Aulacomya atra del Canal Beagle (Tierra del Fuego...