Munida, Leach, 1820

Cabezas, Patricia, Macpherson, Enrique & Machordom, Annie, 2009, Morphological and molecular description of new species of squat lobster (Crustacea: Decapoda: Galatheidae) from the Solomon and Fiji Islands (South-West Pacific), Zoological Journal of the Linnean Society 156 (3), pp. 465-493 : 486-487

GENUS MUNIDA

After alignment with other sequences of the genus Munida determined in a previous study ( Machordom & Macpherson, 2004; Macpherson & Machordom, 2005), 1199 bp were finally analysed. As for the other genera, the 16S rRNA gene showed a high variability region between positions 245 and 272 that required the insertion of gaps. The partial COI sequence data set obtained for the genus Munida consisted of 657 characters, of which 392 were constant, 19 were parsimony uninformative, and 246 were parsimony informative. For the 16S rRNA gene sequence, the resulting data set comprised 542 characters, of which 327 were constant, 50 were parsimony uninformative, and 165 were parsimony informative. Intrageneric divergence for the genus was in the range of 0.69– 13.26% for the 16S rRNA gene, and of 3.50–20.24% for COI. The ILD test revealed no significant incongruence among the gene partitions (P = 0.96), and as for the other genera there were no incongruent topologies, so both genes were analysed in a single matrix. We also analyzed the 16S rRNA gene separately, as the COI gene could not be amplified in some species.

Tests for the 16S rRNA gene rendered no signs of saturation, but the COI gene sequence exhibited a certain level of saturation in transitions when all substitutions were plotted together, and also for third codon positions.

The model that best fitted the combined data set was the K81uf + I + G model (Kimura 3-parameters model; Kimura, 1980), which gave an a- parameter of 0.5357 and an I-value of 0.5253. Base frequencies were A = 0.3893, C = 0.1068, G = 0.0969, and T = 0.4070, and the proportions of changes were 1.0000, 19.4012, 1.5268, 1.5268, and 19.4012. Model HKY + I + G ( Hasegawa, Kishino & Yano, 1985) was selected for the ML analyses.

The model that best fitted the 16S rRNA data set was the TVM + I + G model (transversional model), which gave an a- parameter of 0.6255 and an I-value of 0.4306. Base frequencies were A = 0.3988, C = 0.0698, G = 0.1364, and T = 0.3950, and the proportions of changes were 1.2190, 19.2918, 2.6905, 0.0000, and 19.2918. Model GTR + I + G ( Lavane et al., 1984; Rodríguez et al., 1990) was selected for the ML analyses.

The relationships of the genus Munida with other genera of the family remain unclear, therefore the species Eumunida sternomaculata de Saint Laurent and Macpherson, 1990 was selected as the outgroup, on the basis of previous studies ( Morrison et al., 2002; Machordom & Macpherson, 2004). Analysis of the combined data set (data not shown), and the 16S rRNA data set separately ( Fig. 11 ), indicated two main clusters.

In the combined data set the basal cluster included the species Munida delicata Macpherson, 2004 , and the type species of the genus Munida rugosa (Fabricius, 1775) from the North-East Atlantic, and the second cluster included the rest of the species of the genus. The basal group was supported in all of the analyses, with higher support in the Bayesian analyses than that indicated by the bootstrap. Divergences between these two species were quite high: 8.69% for the 16S rRNA gene and 15.80% for the COI gene. The second cluster was well supported except by the results of the Bayesian analysis.

As the COI gene sequence could not be amplified in the new species M. oblongata sp. nov., as in the species Munida devestiva Macpherson, 2006 , the 16S rRNA gene sequence was analysed separately. In this analysis, these two species appeared in a basal cluster together with the species M. rugosa and M. delicata ( Fig. 11 ). The type species M. rugosa was the sister lineage of the other three species, although bootstrap values and posterior probabilities were low. Divergence was in the range of 8.69–13.06%, which is high compared with that shown by the remaining species of the genus. The second cluster was divided into two different subgroups. All of the newly described species were included in the first subgroup. The species M. lailai sp. nov. appeared as the sister group of the species M. parca with high support. Divergence between these two species was low: 0.69% for the 16S rRNA gene and 4.75% for the COI gene. The species M. caeli sp. nov. was the sister lineage of these two species, also with high support, showing mean divergences of 1.87% (16S rRNA) and 7.45% (COI) from M. parca , and 1.64% and 8.11% from M. lailai sp. nov., respectively. The phylogenetic relationship of the species M. mendagnai sp. nov. was not fully resolved, although in all tree topologies it occupied a basal position in the first subgroup.

Figures

Figure 11. Neighbour-joining (NJ) tree based on the 16S rRNA data set showing phylogenetic relationships among Munida. Numbers above branches indicate bootstrap values for the NJ and maximum parsimony (MP) analyses. Numbers below branches indicate bootstrap values for the maximum likelihood (ML) analyses and Bayesian posterior probabilities (BPPs).