Calyptraeotheres hernandezi, Hernandez-Avila & Campos, 2006

Ocampo, Emiliano H., Robles, Rafael, Terossi, Mariana, Nuñez, Jesús D., Cledón, Maximiliano & Mantelatto, Fernando L., 2013, Phylogeny, phylogeography, and systematics of the American pea crab genus Calyptraeotheres Campos, 1990, inferred from molecular markers, Zoological Journal of the Linnean Society 169 (1), pp. 27-42 : 37

CALYPTRAEOTHERES HERNANDEZI AND CALYPTRAEOTHERES GARTHI

For the pinnotherids analysed herein, the K2P distance between pairs of mitochondrial sequences forms two groups of values with a discrete gap between them (see Fig. 3 ). The lower boundary of the large-distance group of values is almost an order of magnitude greater than the upper boundary of the lower range of values, both in COI and 16S. Indeed, the shortdistance group has no overlap with the large-distance group. The average intraspecific and interspecific K2P values calculated in the present study are similar to those observed for other crustaceans. For example, the intraspecific COI distance computed in 150 crustacean families has an average value of 0.0046 ( Costa et al., 2007), whereas in our study the same parameter reaches only a value of 0.009. For the same families mentioned above, the average interspecific distance is 0.17 ( Costa et al., 2007), whereas in our case it reaches an average value of 0.183. Therefore, the DNA barcode in pinnotherids, as in other crustaceans ( Costa et al., 2007; Puillandre et al., 2011; Negri, Pileggi & Mantelatto, 2012), promises to be a good system to determine the limits amongst species and can be used to complement classical taxonomy.

By contrast, the genetic distances of COI and 16S between specimens of C. hernandezi and C. garthi fall into the short-distance group. The COI sequences between these species differ by only three mutations, which caused, on average, a divergence of 0.010. Likewise, the two 16S sequences of C. hernandezi differ by one mutational step from the 16S of C. garthi . Genetic divergence between 16S sequences of C. hernandezi and C. garthi was on average 0.0036. Therefore, our molecular results do not support a species status for C. hernandezi .

According to Hernández-Ávila & Campos (2006), the most important character distinguishing C. hernandezi from C. garthi is the morphology of the adult third maxilliped, which is two-segmented (dactyl absent) in the former species and three-segmented (dactyl present) in the latter. Three characters can also be used to differentiate C. hernandezi from the northeastern Pacific C. granti : females of C. hernandezi have eyes that are visible in dorsal view, the propodi of the walking legs have subparallel margins, and the ventral margin of the pollex bears a small fringe of setae ( Hernández-Ávila & Campos, 2006). These three features were present in the specimens of C. hernandezi from Cubagua Island, Venezuela, examined in our study. However, it is our opinion that these characters are shared with C. garthi . In this context, Fenucci (1975) mentioned that the margins of the propodi of the first and second walking legs are almost straight in the female of C. garthi , and the illustrations ( Fenucci, 1975: 170) show that these margins are not tapered distally. Additionally, the illustrations of Fenucci (1975) reveal that the female eyes are clearly observed from the dorsal view and that a fringe of setae covers the ventral margin of the pollex. As expected, these three characters were also observed in the specimens of C. garthi included in the present study, therefore contradicting the observations of Hernández-Ávila & Campos (2006).

At this point, we believe that an exhaustive morphological study applying high-resolution techniques (e.g. scanning electron microscopy), accompanied by analysis of more specimens and DNA markers of C. hernandezi , is perhaps necessary to clarify whether C. garthi and C. hernandezi are separate clades or are populations of the same species. For now, our results support the idea that C. hernandezi represents a junior synonym of C. garthi .

Under the hypothesis that C. hernandezi and C. garthi belong to a single species, the question arises as to whether there is genetic flow between these two putative populations of C. garthi . Calyptraeotheres garthi occurs in the south-western Atlantic Ocean from San Matias Gulf, Argentina, to Rio Grande do Sul, Brazil ( Martins & D’Incao, 1996), whereas C. hernandezi is known only from Cubagua Island, Venezuela. Between the northern boundary of the former species and the location of the latter is a geographical gap of ~ 6400 km. The coast of Brazil harbours a large number of potential (see Simone, 2006) and probable (e.g. the limpet Bostrycapulus odites Collin, 2005 ; Ocampo et al., 2012) hosts of Calyptraeotheres . Nevertheless, there is no record of Calyptraeotheres from intermediate sites between southern Brazil and Venezuela. Attempts to obtain Calyptraeotheres from intermediate areas through examination of scientific collections (the museums of Rio Grande do Norte; LABOMAR, Fortaleza, Recife; MOUFPE, Recife; UESC, Bahia; MNRJ, Rio de Janeiro; MZUSP, São Paulo; and MACN, Buenos Aires), sampling on the coast of São Paulo and Rio de Janeiro, Brazil (hosts: Crepidula sp. and Bostrycapulus odites present but with no crabs associated), and also consultation of a malacologist who studies potential hosts of Calyptraeotheres (L. Simone, pers. comm.), were unsuccessful. Apparently, Calyptraeotheres are absent from this area or, perhaps, are present only at low levels of abundance. Therefore, C. hernandezi and C. garthi appear to be genetically isolated, and the single-species hypothesis becomes weak and difficult to credit. Alternatively, there may have been a recent speciation event, which could explain the low genetic distance observed above. By contrast, the lack of genetic differentiation between C. garthi and C. hernandezi could be a consequence of the introduction of specimens, either in the larval stage through ballast water or in the adult stage along with some of the multiple hosts ( Ocampo et al., 2012), as has been observed in other marine organisms ( Reise, Gollasch & Wolff, 1992; Orensanz et al., 2002), including decapods ( Hidalgo, Barón & Orensanz, 2005; Taylor & Komai, 2011).

Figures

Figure 3. Histogram of Kimura two-parameter genetic distances for (A) the cytochrome oxidase I and (B) the large ribosomal subunit (16S) data sets. Species and number of specimens used for intraspecific and interspecific distance calculations are detailed in Table 1.