Integrative species delimitation
Integrating molecular and phenotypic data using different methodologies
is widely assumed to be the most effective approach for delimiting
species (Dayrat 2005; Will et al. 2005; Schlick-Steiner et al. 2010;
Pante et al. 2015). Integrative taxonomy provides statistical rigor for
species delineation and validation of species, as well as for assignment
of specimens to a given species group, improving the detection of
cryptic diversity and the inference of relationships among species
(Leaché and Fujita 2010; Schlick-Steiner et al. 2010; Edwards and
Knowles 2014; Leavitt et al. 2015). This approach allows the
identification of concordant patterns of divergence based on different
sources of information (e.g. unlinked genetic loci, morphology,
behavior), thus revealing cases of full lineage separation, since it is
highly unlikely that a coherent pattern of character agreement emerges
by chance (Padial et al. 2010).
Our molecular-based analyses using the cox1 , 3RAD and UCEs data
sets, together with analysis of CHC variation, yielded strongly
congruent evidence for the existence of five different evolutionary
lineages among the examined populations of E. ruidum . Our results
support the existence of the four species suggested by Aguilar-Velasco
et al. (2016) (E. ruidum spp. 1-4) and also a fifth species
corresponding to what they suggested to be a hybrid population (E.
ruidum 2x3). Four of these species were found in localities situated
along the lowlands of the Sierra Madre del Sur in Oaxaca and Guerrero,
Mexico. Moreover, the possibility of a sixth species in the area is
plausible according to recent chemical, genetic and acoustic studies
(Peña-Carrillo et al. 2021a, b).
We consistently recovered the specimens assigned to E. ruidum sp .
1 as a well-differentiated species, regardless of the data set and
analyses employed. Our CHC and cox1 -based network showed the
members of E. ruidum sp. 1 as a highly divergent cluster whose
geographic distribution ranges from southeast Mexico to Ecuador,
Colombia and Venezuela in South America, and in the Lesser Antilles in
the Caribbean. This network also showed the existence of geographic
structure within this species. The name E. ruidum should be
applied to the populations assigned to E. ruidum sp. 1 based on
the type locality of the species, which was restricted to Colombia by
Kugler and Brown (1982), and on their morphological correspondence with
the syntypes from this country (Aguilar-Velasco et al. 2016). The 3RAD,
UCE and cox1 analyses also recovered the specimens of E.
ruidum sp. 2 as a separate species, being composed of two
geographically structured clades. One of these clades included specimens
from southeast Mexico to Colombia and Ecuador in South America, whereas
the other one was represented by specimens from southeast to northern
Mexico. The cox1 data set, however, showed a considerable genetic
distance between these clusters, suggesting that they could be separate
species. This hypothesis is supported by the CHC analyses, which also
showed a marked divergence between the two clades.
The remaining three species delimited here correspond to populations
from the lowlands of Sierra Madre del Sur in the states of Oaxaca and
Guerrero, in southeast Mexico. The two genome-wide data sets and the CHC
profiles indicated that E. ruidum sp. 3 and E. ruidum sp.
4 are two closely related species whose geographic distribution is
restricted to lowland areas of Oaxaca. Moreover, our results
consistently support the hypothesis that the specimens of the putative
hybrid population proposed by Aguilar-Velasco et al. (2016) from
Pinotepa Nacional, Oaxaca, and those assigned to E. ruidum sp. 3
from the state of Guerrero, actually represent a distinct species.
Further comprehensive sampling on foothills along the Pacific coast in
southeast Mexico will reveal the actual geographic distribution of these
three species. Moreover, taxonomic inferences based on these results
should consider the previous name availability within the group.Ectatomma aztecum was described by Emery (1901) based on a single
specimen collected in the state of Michoacán, Mexico, but without
precise locality; however, it was subsequently regarded as a synonym ofE. ruidum by Kugler and Brown (1982). According to
Aguilar-Velasco et al. (2016) the syntype of E. aztecum(CASENT0903841; MSNG, Genoa, Italy) is morphologically similar to the
specimens assigned to E. ruidum sp. 3.