Agononida (Machordom & Macpherson, 2004)

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 : 484

GENUS AGONONIDA

After alignment with other sequences determined for the genus Agononida in a previous study ( Machordom & Macpherson, 2004), 1187 bp were finally examined. The 16S rRNA sequence showed a high variability region between positions 245 and 272, which required the insertion of gaps. The partial COI sequence data set obtained consisted of 657 characters, of which 428 were constant, 29 were parsimony uninformative, and 200 were parsimony informative. For the 16S rRNA gene sequence, the resulting data set comprised 530 characters, of which 381 were constant, 22 were parsimony uninformative, and 127 were parsimony informative. Saturation tests indicated no saturation when we plotted all the substitutions together, but revealed saturation for transitions in the third codon positions of the COI gene for divergence values above 15%.

Intrageneric divergences between the new species and known species of the genus Agononida were in the range of 3.40–13.10% for 16S rRNA, and 8.70– 17.88% for the COI gene. The new species showed the least divergence from A. similis : 3.40% for the 16S rRNA and 8.70% for the COI. The incongruence length difference (ILD) test revealed no significant incongruence among gene partitions (P = 0.45), and there were no strongly supported conflicting nodes among the tree topologies, so both genes were analysed in a combined data set, and only these results are presented.

The model that fitted the combined data set best was the GTR + I + G model (general time-reversible model; Lavane et al., 1984; Rodríguez et al., 1990), which gave an a- parameter of 1.3220 and an I-value of 0.5680. Base frequencies were A = 0.3220, C = 0.1480, G = 0.1739, and T = 0.3560, and the proportions of changes were 1.5688, 7.3481, 2.8003, 0.2082, and 16.2166. The selected outgroup was Crosnierita dicata (Macpherson, 1998) , which was the closest genus to Agononida ( Machordom & Macpherson, 2004) . The species Alainius crosnieri Baba, 1991 was also included to test for a non-monophyletic origin of the genus. Relationships at terminal nodes were highly supported by bootstrap and posterior probability values ( Fig. 9 ). At deep nodes, relationships were unresolved, and there was no support for the monophyly of the genus Agononida , but the new species in this genus was highly supported. Relationships among the different species exhibited a first cluster including A. isabelensis sp. nov. + A. similis , which was highly supported in all of the analyses. The sister group of this cluster was Agononida procera Ahyong and Poore, 2004 , which was supported by all of the analyses. The species Agononida marini ( Macpherson, 1994) appeared as a sister group of these three species, although support for this position was very low. The phylogenetic positions of the species Agononida sphecia ( Macpherson, 1994) and Agononida incerta (Henderson, 1888) were not resolved.

Figures

Figure 9. Neighbour-joining (NJ) tree based on the combined data set (16S rRNA and COI genes) showing phylogenetic relationships among Agononida. 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).