DIMORFISMO SEXUAL EN TAMAÑO Y FORMA EN UNA POBLACIÓN DE ESCÍNCIDOS DE COLA AZUL DEL GÉNERO Plestiodon (SCINCIDAE) / Sexual size and shape dimorphism in a population of blue-tailed skinks of the genus Plestiodon (Scincidae)

RESUMEN En este estudio, investigamos el dimorfismo sexual en el tamaño corporal (longitud hocico cloaca) y rasgos morfológicos (cabeza, cuello, tronco y extremidades) en una población de escíncidos pertenecientes a una especie recién descubierta del género Plestiodon. Además, se determinaron las trayectorias alométricas de los rasgos corporales que mostraron dimorfismo sexual y se discute su importancia en la expresión de las diferencias sexuales encontradas. Se realizó una prueba de t de student para detectar diferencias significativas en la LHC y se siguió un enfoque multivariado para investigar el dimorfismo sexual en los otros caracteres examinados. Se utilizó regresión por ejes principales reducidos (SMA) para determinar las trayectorias alométricas correspondientes. No se detectó dimorfismo sexual en la longitud hocico cloaca y masa corporal. La longitud y ancho de la cabeza, la longitud del cuello y la longitud de las extremidades traseras fueron mayores en machos que en hembras; en contraste, se encontró el patrón opuesto en el caso de la longitud del tronco (axila-ingle). Se detectaron relaciones isométricas, así como alométricas positivas y negativas entre los rasgos analizados. Sin embargo, únicamente el dimorfismo sexual en el ancho de la cabeza fue afectado por sus trayectorias de crecimiento.

ABSTRACT In this study, we investigated sexual dimorphism in body size (snout-vent length) and morphological traits (head, neck, trunk, and limbs) in a population of skinks belonging to a newly discovered species of genus Plestiodon. In addition, we determined the allometric trajectories of body traits that showed sexual dimorphism and discussed their importance in the expression of the sexual differences found. A Student's t-test was performed to detect different significant in the SVL and a multivariate approach was followed to investigate sexual dimorphism in the other characters examined. Reduced major axis regression (SMA) were used to determine the corresponding allometric trajectories. No sexual dimorphism was detected in the snout-vent length and body mass. The length and width of the head, the length of the neck and the length of the hind limbs were greater in males than in females; by contrast, the opposite pattern was found in the case of trunk length. Isometric relationships were detected, as well as positive and negative allometric relationships between the traits analyzed. However, only sexual dimorphism in the head width was affected by their growth trajectories.

Integrative species delimitation in practice: Revealing cryptic lineages within the short-nosed skink Plestiodon brevirostris (Squamata: Scincidae).

Integrative taxonomy has been generally considered as a goal in systematics for more than a decade. Here, we employed environmental, molecular, and morphological data to evaluate the species boundaries within the short-nosed skink Plestiodon brevirostris from south-central Mexico, one member of the morphologically conservative P. brevirostris group. Our molecular dataset includes one mitochondrial and two nuclear loci. The mitochondrial fragment includes the full length of the gene coding for the NADH dehydrogenase subunit 1 protein, a segment of the gene coding for 16S ribosomal RNA, and flanking tRNAs. The nuclear dataset includes fragments of the genes coding for the megakaryoblastic leukemia 1 and RNA fingerprint 35 proteins. We employed phylogenetic reconstruction, analyses of population structure and morphological variation, and species delimitation methods (including the integration of the three kinds of data in a unified probabilistic framework) to evaluate species limits. Our results suggest that P. brevirostris represents four distinct species. The information provided by each kind of data allowed us to discern between alternative explanations for the observed patterns of geographic structure. Two of the newly recognized lineages are poorly differentiated morphologically but apparently differ in environmental preferences and are allopatric. Additionally, one lineage is microendemic and parapatric with respect to another one. Moreover, our phylogenetic analyses suggest that other taxa within the P. brevirostris group may represent species complexes. We discuss our results in the context of integrative species delimitation.

Anolis boulengerianus Thominot, 1887, a senior synonym of Anolis isthmicus Fitch, 1978 (Squamata: Dactyloidae).

For most of its history, the name Anolis boulengerianus Thominot, 1887 has been regarded as a junior synonym of Anolis nebulosus (Wiegmann, 1834) or Anolis nebuloides Bocourt, 1873. However, a comparison of the syntypes and additional topotypical specimens of A. boulengerianus with three topoparatypes and additional specimens of the species currently referred to as Anolis isthmicus Fitch, 1978 showed that these two names pertain to the same species. Because of the priority principle, A. isthmicus becomes a junior synonym of A. boulengerianus. We provide a redescription of the type series of A. boulengerianus and an updated diagnosis for this taxon relative to all other beta anoles.

Accommodating heterogenous rates of evolution in molecular divergence dating methods: an example using intercontinental dispersal of Plestiodon (Eumeces) lizards.

Identifying and dating historical biological events is a fundamental goal of evolutionary biology, and recent analytical advances permit the modeling of factors known to affect both the accuracy and the precision of molecular date estimates. As the use of multilocus data sets becomes increasingly routine, it becomes more important to evaluate the potentially confounding effects of rate heterogeneity both within (e.g., codon positions) and among loci when estimating divergence times. Here, using Plestiodon lizards as a test case, we examine the effects of accommodating rate heterogeneity among data partitions on divergence time estimation. Plestiodon inhabits both East Asia and North America, yet both the geographic origin of the genus and timing of dispersal between the continents have been debated. For each of the eight independently evolving loci and a combined data set, we conduct single model and partitioned analyses. We found that extreme saturation has obscured the underlying rate of evolution in the mitochondrial DNA (mtDNA), resulting in severe underestimation of the rate in this locus. As a result, the age of the crown Plestiodon clade was overestimated by 15-17 Myr by the unpartitioned analysis of the combined loci data. However, the application of partition-specific models to the combined data resulted in ages that were fully congruent with those inferred by the individual nuclear loci. Although partitioning improved divergence date estimates of the mtDNA-only analysis, the ages were nonetheless overestimated, thus indicating an inadequacy of our current models to capture the complex nature of mtDNA evolution in over large time scales. Finally, the statistically incongruent age distributions inferred by the partitioned and unpartitioned analyses of the combined data support mutually exclusive hypotheses of the timing of intercontinental dispersal of Plestiodon from Asia to North America. Analyses that best capture the rate of evolution in the combined data set infer that this exchange occurred via Beringia ∼18.0-30 Ma.

Bermuda as an evolutionary life raft for an ancient lineage of endangered lizards.

Oceanic islands are well known for harboring diverse species assemblages and are frequently the basis of research on adaptive radiation and neoendemism. However, a commonly overlooked role of some islands is their function in preserving ancient lineages that have become extinct everywhere else (paleoendemism). The island archipelago of Bermuda is home to a single species of extant terrestrial vertebrate, the endemic skink Plestiodon (formerly Eumeces) longirostris. The presence of this species is surprising because Bermuda is an isolated, relatively young oceanic island approximately 1000 km from the eastern United States. Here, we apply Bayesian phylogenetic analyses using a relaxed molecular clock to demonstrate that the island of Bermuda, although no older than two million years, is home to the only extant representative of one of the earliest mainland North American Plestiodon lineages, which diverged from its closest living relatives 11.5 to 19.8 million years ago. This implies that, within a short geological time frame, mainland North American ancestors of P. longirostris colonized the recently emergent Bermuda and the entire lineage subsequently vanished from the mainland. Thus, our analyses reveal that Bermuda is an example of a "life raft" preserving millions of years of unique evolutionary history, now at the brink of extinction. Threats such as habitat destruction, littering, and non-native species have severely reduced the population size of this highly endangered lizard.