Morphological analysis and description of two new species of Rhogeessa (Chiroptera: Vespertilionidae) from the neotropics

2012·1.8 MB·English

by  Baird, Amy B.

TEXAS TECH UNIVERSITY
Natural Science Research Laboratory
Occasional Papers
Museum of Texas Tech Univers
Number 307 12 January 2012
Morphological Analysis and Description of Two New
Species of Rhogeessa (Chiroptera: Vespertilionidae) from
the Neotropics
Front cover: Rhogeessa bickhami, new species (left) and Rhogeessa menchuae, new species (right) collected in
Guatemala. Photographs courtesy of John W. Bickham.
Morphological Analysis and Description of Two New Species of Rhogeessa
(Chiroptera: Vespertilionidae) from the Neotropics
Amy B. Baird, Maria R. Marchan-Rivadeneira, Sergio G. Perez, and Robert J. Baker
Abstract
We recognize and formally name two new species within the Rhogeessa tumida complex
based primarily on a genetic concept of species. Using genetic and morphological data we
estimate species boundaries of the newly named taxa. Consistent genetic evidence in mtDNA,
as well as autosomal and Y chromosome markers, indicate the presence of three distinct genetic
lineages within what had been considered R. tumida. Morphologically, the two new species are
similar, with small differences in skull proportion. Morphological distinctiveness among the
members of the R. tumida complex is difficult to delineate and this has resulted in a historically
intricate taxonomy. Based on available data, one of the new species is distributed mainly along
the Pacific versant of Mexico and Central America. The second new species is distributed on
the Atlantic versant of Central America in Guatemala, Honduras, and perhaps Nicaragua. These
additions bring the number of species in the R. tumida complex to eight, the others being R.
aeneus, R. genowaysi, R. hussoni, R. io, R. tumida, and R. velilla.
Key words: cryptic species, morphology, phylogenetics, Rhogeessa tumida complex,
taxonomy
Resumen
Nosotros reconocemos y formalmente nombramos dos nuevas especies dentro del complejo
Rhogeessa tumida basados principalmente en el concepto genetico de especies. Utilizando
informacion tanto genetica como morfologica nosotros estimamos los limites especificos de
los nuevos taxones. Evidencias geneticas consistentes en marcadores de ADN mitocondrial,
cromosomas autosomicos y cromosoma Y indican la presencia de tres linajes geneticos distintos
dentro de lo que ha sido considerado el complejo R. tumida. Morfologicamente, las dos nuevas
especies son similares, con pequenas diferencias en las proporciones craneales. La diferenciacion
morfologica entre los miembros del complejo R. tumida es dificil de delinear y esto ha resultado
en una taxonomia historicamente complicada. Basados en los datos disponibles, una de las
nuevas especies se distribuye a lo largo de la vertiente del Pacifico de Mexico y Centroamerica.
La segunda nueva especie esta distribuida a lo largo de la vertiente Atlantica de Centroamerica
en Guatemala, Honduras, y posiblemente Nicaragua. Estas adiciones elevan el numero de espe¬
cies en el complejo R. tumida a ocho, siendo las otras R. aeneus, R. genowaysi, R. hussoni, R.
io, R. tumida, y R. velilla.
Palabras claves: complejo Rhogeessa tumida, especies cripticas, filogenia, morfologia,
taxonomia
2 Occasional Papers, Museum of Texas Tech University
Introduction
Determining what constitutes a species is one of several decades. Since LaVal’s (1973) morphological
the most difficult and controversial problems faced by study of the genus Rhogeessa, in which he considered
biologists studying biodiversity. Numerous different all members of this complex to be a single species, five
species concepts have been proposed in the last century, additional species have been described. Currently, the
each of which has received considerable attention and species complex, in addition to R. tumida, consists of
debate. When putative species show no morphological R. aeneus, R. genowaysi, R. io, R. velilla, and R. hus-
differences and reproductive behaviors are not known, soni (Baker 1984; Audet et al. 1993; Genoways and
the task of determining the proper taxonomy is even Baker 1996; Baird et al. 2008). In general, the newly
more difficult. One concept in particular, the Genetic described species were found to be morphologically
Species Concept (GSC) (Baker and Bradley 2006), difficult to differentiate from one another, but all dif¬
proposes a method of identifying species regardless of fered karyotypically, with the exception of identical
whether morphological or behavioral differences have karyotypes shared between R. genowaysi and R. velilla
evolved or have been documented to distinguish them. (Baird et al. 2008). Baird et al. (2008, 2009) also
In the Genetic Species Concept (Baker and Bradley demonstrated that all of these species, including R.
2006), species are recognized as distinct when they genowaysi and R. velilla, were genetically distinct from
have attained a level of genetic differences expected one another based on nuclear and mtDNA sequence
to produce incompatibility between the respective data. Whereas LaVal (1973) did not distinguish all of
genomes of each. the current members of the R. tumida complex based
on morphology, he did demonstrate that there was
The Genetic Species Concept is conceptually exceptional morphological variation present within
founded on genetic incompatibilities producing an iso¬ what he considered to be a single species. More recent
lating mechanism in genetically diverged phylogroups. comprehensive morphological analyses have not been
The GSC is a consistent method of identifying species performed on this group following the description of
across various taxonomic groups with the support of additional species, so it remains unclear whether the
a database of genetic information. Hypotheses of variation found by LaVal (1973) is simply intra-specific
genetic incompatibility can be tested rigorously and variation, or whether the variation may correspond with
independently by using multiple genetic markers or genetic limits of newly defined species.
other types of studies such as breeding cycles, morphol¬
ogy, and ecology. This concept allows cryptic species Baird et al. (2008, 2009) found consistent ge¬
to be identified more easily and accurately, which is netic evidence in mtDNA, as well as autosomal and
important for understanding biological diversity and Y chromosome markers for multiple distinct lineages
describing species and their geographic boundaries. of what is currently referred to as the single species,
There are several examples in mammals of cryptic spe¬ R. tumida (Genoways and Baker1996). Their genetic
cies being described based on genetic differences in the data showed a distinct lineage from the Pacific versant
absence of morphological variation (e.g., Hellborg et al. of Mexico and Central America, a second lineage from
2005, Baker and Bradley 2006). Additionally, genetic the Atlantic versant of Mexico, and a third lineage from
data can establish monophyletic lineages, and uncover the Atlantic versant of Central America. None of these
a lack of gene flow and/or genetic variation between DNA sequence-based datasets (mtDNA - Baird et al.
morphologically divergent groups to better establish a 2008; nuclear - Baird et al. 2009) indicated evidence for
genetically well defined biodiversity of mammal spe¬ genetic introgression between any of the three lineages
cies (Lausen et al. 2008; Larsen et al. 2010). of R. tumida. Therefore, the authors hypothesized that
the three genetic lineages may each represent distinct
One group of mammals that exhibits high species species as defined by the Genetic Species Concept.
diversity despite a lack of morphological differentiation
is the Rhogeessa tumida complex (Chiroptera: Vesper- The genetic divergence between the different
tilionidae). Members of the R. tumida species complex lineages of R. tumida is significant. With cytochrome-/)
have undergone many taxonomic changes in the last (Cytb), Baird et al. (2008) reported a genetic difference
Baird et al.—Two New Species of Rhogeessa 3
of about 10% (K2P) between the Pacific and each cies R. bombyx (Genoways and Baker 1996; Simmons
Atlantic lineage. The two Atlantic lineages differed 2005). Therefore, based on our search of the literature,
from one another by about 2.5% at that locus. With no species-level available names are applicable to the
ZFY (Y chromosome locus), Baird et al. (2009) found new putative species.
that the Atlantic Mexican R. tumida and Pacific R.
tumida (along with R. aeneus) shared a single hap- The type specimen of R. tumida is from Mirador
lotype, whereas the Central American R. tumida was in Veracruz, Mexico (Allen 1866). This locality is near
distinct. With MPI (autosomal locus), Baird et al. the Atlantic coast of Mexico, in the closest geographic
(2009) showed, again, that the Pacific R. tumida group proximity to the genetic “Atlantic Mexican R. tumida
was quite distinct from the other two, but did not form lineage” of Baird et al. (2008, 2009).
a statistically supported monophyletic group at this
locus. The degree of differentiation found in between The taxonomy of the Rhogeessa tumida complex
the Pacific and Atlantic lineage is about the level con¬ has been exceptionally difficult to resolve. This paper
sistent with between-species comparisons in many is intended to examine all available data with respect
mammalian groups (Bradley and Baker 2000). The to members of that complex in order to determine the
difference between the two Atlantic lineages is lower geographic structure of species boundaries. We review
in Cytb, more typical of species within Platyrrhinus available genetic data (nuclear and mtDNA sequences
(Velazco et al. 2008). However, each is evidently an and karyotypes) in the context of the Genetic Species
independently-evolving monophyletic group based on Concept (Baker and Bradley 2006). Additionally, we
total evidence from mtDNA and nuclear loci. examine in more detail the presence or absence of mor¬
phological differentiation between lineages currently
Examination of the availability of species-level classified as R. tumida. Specifically, we examine the
names from populations of the genetically distinct morphometric variation of the three genetic lineages of
Central American R. tumida taxon, a previously de¬ R. tumida presented in Baird et al. (2008, 2009). We
scribed subspecies of R. tumida, R. tumida major, is also review the taxonomy of R. tumida and formally
now considered to be a synonym of R. parvula based describe two of the distinct genetic lineages of what
on morphology (LaVal 1973; Simmons 2005). Another were previously classified as R. tumida as distinct
previously described subspecies of R. tumida, R. tumida species.
riparia, is now a synonym of R. io, as is the former spe-
Materials and Methods
Morphometric data.—Twenty specimens referred information and included: overall total length (TL);
to as the “Pacific R. tumida lineage” and “Central length of tail (LT); length of hind foot (LHF); and length
American R. tumida lineage” by Baird et al. (2008, of ear (LE). Six cranial and mandibular measurements
2009) were examined using linear morphometric were taken to the nearest 0.01 mm with a digital caliper.
analyses (n = 17 and n = 3, respectively). In addition, Cranial and mandibular measurements were selected
seventeen specimens of six species of Rhogessa were following LaVal (1973) with additions as noted below:
used as comparative material (Appendix I). All the greatest length of the skull (GLS—including incisors);
specimens examined had been studied genetically (Fig. condylobasal length (CBL); mastoid width (MW);
1; also see Baird et al. 2008,2009), with the exception depth of the braincase (DB); zygomatic width (ZW);
of additional material of R. genowaysi and R. parvula. postorbital width (POW); width across first upper ca¬
For our purposes, it was critical to examine specimens nines (C1-C1); width across first upper incisors (II-II);
that had been identified genetically due to the known width across second upper molars (M2-M2); maxil¬
morphological similarity of other Rhogeessa species. lary length (MAXL); maxillary toothrow (MAXT);
This reduced our sample size, but it removed the palatal length (PL); mandible length (ML—including
possibility of any identification errors. Four external incisors); coronoid height (CH); mandibular toothrow
measurements were recorded of skin tags or field notes (MAND); and width across first lower canines (cl-cl).
4
Occasional Papers, Museum of Texas Tech University
R. aeneus + 2 R. menchuae
R. menchuae
R. tumida
R. velilla
A.
R. bickhami
R. genowaysi
R. io
outgroups
R. tumida, R. aeneus, R. bickhami
R. menchuae
B. R. velilla
R. io
outgroups
R. aeneus
R. velilla
R. tumida + 1 R. aeneus
R. menchuae
j-
c. R. bickhami
R. genowaysi
R. io
outgroups
Figure 1. Representative phylogenies from previous genetic studies. A) phylogeny based on
mtDNA cytochrome-/) sequences; B) phylogeny based on Y-chromosomal ZFY sequences
(note that no male R. genowaysi was included in this phylogeny); C) phylogeny based on
nuclear MPI sequences. In these figures, all major clades have been collapsed into a single
lineage. For more detailed phylogenies, see Baird et al. (2008, 2009).
Baird et al.—Two New Species of Rhogeessa 5
Descriptive statistics (including mean, standard devia¬ referred as PC). All analyses were conducted using
tion, and range) of external, cranial, and mandibular MATLAB (version 6.5, The Mathworks) and SPSS
measurements were calculated for all species. (version 16.0.1, SPSS Inc.).
Multivariate analysis.—Only cranial and Phylogenetic relationships.—We examined the
mandibular measurements were used in multivariate phylogenies of Rhogeessa presented in Baird et al.
analyses to eliminate measurement error (Blackwell et (2008, 2009). We examined the sequences used to
al. 2006). A MANOVA test was used to assess mor¬ generate those phylogenies to find fixed nucleotide
phometric differences in all 16 measurements among differences between taxa. We also reviewed all avail¬
species. Alpha levels were adjusted using a Bonfer- able karyotypic (Bickham and Baker 1977; Baker et
roni correction for multiple tests. Additionally, we al. 1985), allozyme (Baker et al. 1985), and previous
performed a principal component analysis (PCA) on morphological analyses in the genus (LaVal 1973). The
the covariance matrix of log-transformed cranial and purpose of gathering all available phylogenetic data is
mandibular measurements to establish the variation in to examine evidence for monophyly of putative new
the sample examined. Skull size variation in the sample species of Rhogeessa.
was summarized by the first two axes of PC A (hereafter
Results
Results of a MANOVA test showed that two of velilla and R. io were partially separated with respect to
16 cranial and mandibular measurements (zygomatic the remainder of the species primarily along the PC2.
width and postorbital width) were significantly differ¬
ent among species of Rhogeessa (P < 0.05; Table 1). All DNA sequence data previously published on
Mean values of zygomatic width were higher in R. Rhogeessa (Baird et al. 2008, 2009) indicate that all
tumida sensu stricto, R. velilla, and R. io; and lower in members of the R. tumida complex, including the two
R. aeneus with respect to genetically identified phylo- putative new species are reciprocally monophyletic
groups of the respective “Pacific and Central American entities (Fig. 1; Table 3). There is one instance of
R. tumida lineages” (Table 1). possible ancient hybridization between R. tumida and
R. aeneus (Baird et al. 2009), but the phylogenetic pat¬
A PCA of 16 cranial and mandibular measure¬ terns may also be a result of incomplete lineage sorting
ments performed for 37 specimens found that the first at the loci examined. Cytochrome-6 sequences were
two principal components accounted for 59.1% of examined for unique, fixed differences between species
the total variation in the sample (33.7% and 25.4%, (Appendix II). These data show that each species has
respectively; Table 2). PCI was highly and positively unique, diagnostic variation in this gene.
correlated with all measurements and was therefore
interpreted as an overall size variation vector. Along Morphological analyses presented in this paper
PC 1 and PC2 the variables that accounted for most of showed that the morphometric independence among
the variation were the greatest length of skull and depth species of Rhogeessa is ambiguous and intricate. Mor¬
of the braincase, respectively (Table 2). phometric overlap in cranial and mandibular variables
complicated characterizing the two genetically distinct
Morphometric size variation among all species lineages within the R. tumida complex (Tables 1 and
of Rhogeessa was continuously distributed along PCI 4). However, based on previous DNA sequence data
with an overlapping area in the morphological space and karyotypes (Baird et al. 2008, 2009; Fig. 1) that
(Fig. 2). Specimens of the undescribed “Pacific and document a lack of evidence for genetic exchange
Central American R. tumida lineages” were mainly between lineages of “R. tumida,” we conclude that the
overlapping with respect to the rest of the species along proper action to best describe the biodiversity in the
the first two principal components. Individuals of R. Rhogeessa tumida complex is to recognize these genetic
entities as species.
Occasional Papers, Museum of Texas Tech University
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8 Occasional Papers, Museum of Texas Tech University
Table 2. Percentage of variance explained and factor loadings for
the first two principal components (PCs) of the analysis of 16 cranial
and mandibular measurements. Variables were loglO-transformed
and a covariance matrix was usedfor the analysis. Acronyms for the
variables are explained in the Materials and Methods.
Variable PC 1 PC 2
GLS 0.81 0.24
CBL 0.75 0.32
MW 0.69 0.22
DB 0.39 0.76
ZW 0.32 -0.57
POW 0.01 -0.06
Cl-Cl 0.70 0.32
11-11 0.75 -0.12
M2-M2 0.60 0.29
MAXL 0.72 -0.63
MAXT 0.63 0.22
PL 0.54 0.31
ML 0.55 0.56
CH 0.45 0.59
MAND 0.53 0.28
cl-cl 0.49 0.31
% Variance 33.7 25.4