The role of head shape and trophic variation in the diversification of the genus Herichthys in sympatry and allopatry.

In the present study we evaluated the putative cases of sympatric speciation in the genus Herichthys by studying the variation in head shape using principal component analysis, phylomorphospace and reconstructions of the ancestral states of feeding preferences. Herichthys includes both allopatric and sympatric sister species, as well as sympatric unrelated species and thus offers great potential for evolutionary studies of putatively sympatric speciation. Herichthys is the northernmost group of cichlids in America and one of the most ecologically disparate genera within Middle American cichlids. Fifteen anatomical points were recorded on the heads of 293 specimens of the 11 species recognized within the genus. The results show that in spite of having wide variation in consumed diets, most species of Herichthys are close in morphospace. However, morphological variation was great among the two pairs of sympatric sister species in agreement with the suggested sympatric model of speciation.

Cranial modification and the shapes of heads across the Andes.

This broad literature review considers advances in the study of cranial vault modification with an emphasis on investigations of Andean skeletal remains over the last two decades. I delimit three broad categories of research, building on Verano's synthesis of the state of Andean paleopathology in 1997. These are associations with skeletal pathological conditions, classification and morphology, and social identity. Progress is noted in each of these areas with a particular emphasis on methodological advances in studying morphology as well as the growth of contextualized bioarchaeology and the incorporation of social theory in the consideration of cranial modification as a cultural practice. The article concludes with avenues for future research on head shaping in the Andes specifically and paleopathology more broadly.

Sexual dimorphism, ontogeny and static allometry of a semi-fossorial snake (genus Atractus)

Sexual dimorphism in snakes has been mainly evaluated for size and number of some morphological traits, but few studies address on sexual shape dimorphism. Here we evaluated the existence of sexual size and shape dimorphism in the semi-fossorial snake Atractus reticulatus. We use linear and geometric morphometrics to evaluate differences between sexes and among different ontogenetic stages (neonates, juveniles and adults). We have shown that A. reticulatus is sexually dimorphic for some traits such as body length and head shape, with females being larger and having more robust heads than males, but the sexes do not differ in head size. Males and females are sexually dimorphic in head shape even in neonates, suggesting that this differentiation is prenatal. Differences in head shape may be associated with trophic segregation, allowing females to feed on larger prey than males. Body size dimorphism progressively increases throughout the ontogenetic stages, which is possibly related to the late sexual maturation of females and/or different growth rates between the sexes. We also found that males and females shows some sex-specific patterns towards static and ontogenetic allometry, with males showing stronger predictive response on static allometry than females, whereas females have ontogenetic allometry, but males do not. Additionally, the allometric slopes in A. reticulatus between sexes converge by presenting similar shapes as head size increases, an expected result for sexes with similar lifestyles. Further investigation on some physiological and natural history aspects in Atractus will be particularly useful for a better understanding of the significance of the morphological differences found in this study.

Morphological variation and sexual dimorphism in two sympatric dipsadine snakes from Southern Brazil

Snakes have high morphological variation, including between sexes. Most of these variations are evidenced only by linear measurements, which are generally restricted to size traits. Using traditional and geometric morphometrics methods we analyze how body size attributes and head size and shape varies between sexes and species of two sympatric Tachymenini snakes, Thamnodynastes strigatus and Tomodon dorsatum. We took body size measurements from 87 specimens of T. strigatus and 83 specimens of T. dorsatum. We also extracted head shape and size of 146 specimens of T. strigatus and 156 specimens of T. dorsatum. Our results showed sexual differences in some body size attributes and in head shape and size. Females of both species had larger SVL, BM, HW, BW and heads than in males. But, T. strigatus is not sexually dimorphic in head size. Females of the T. strigatus also exhibited an enlargement of the parietal region compared to the males, while T. dorsatum females exhibited a wider snout than males. These sexual differences could be a result of fecundity selection and may also indicate that females consume larger preys than conspecific males. At the species level, T. strigatus is larger in body and head size than T. dorsatum. The head shape of T. strigatus is characterized by a more elongated head with larger frontal and prefrontal scales and slender snout compared to T. dorsatum. Shape differences between these two snakes probably evolved in association with divergences in habitat use e.g. terrestrial and arboreal and diet specialization e.g. piscivory, and malacophagy.

Head shape variation in cerambycid saproxylic beetles as a function of host plant selection.

Saproxylic insects depend on deadwood for larval development, and a certain degree of specialization may be involved in their choice of host plants and/or wood in a particular stage of degradation. The plant species chosen for oviposition in turn act as an environmental pressure on the head morphology of larvae and it is expected that head shape plasticity varies directly with the number of woody plant species used for larval development in each insect species. We analyzed head shape variation in saproxylic beetles with respect to host plant species, maximum time of larval emergence and season of the year when insects colonized branches. Generalist species in the use of host plants showed significant variation in head shape and size. Time of emergence and season did not appear to affect head shape, although season was a determinant factor of abundance and possibly head size variation.

Cephalic morphological variation in freshwater silversides Odontesthes hatcheri and Odontesthes bonariensis in Patagonia: introgression and ecological relationships.

Based on geometric morphometrics and discriminant analysis, the percentage of silverside Odontesthes hatcheri and Odontesthes bonariensis individuals identified by a taxonomic key and misclassified by discriminant analysis was obtained and a negative correlation between the percentage of misclassified individuals of O. hatcheri and the distance to the nearest hatchery stocking silversides was found, suggesting a genetic introgression. Morphological analyses between species, between populations and within populations pointed to the same anatomical structures, suggesting a nested variation related to environmental cues such as availability of littoral shelter. The dependence between the cephalic morphology of O. hatcheri and body size would be in agreement with the trophic niche shifts of the species. Introgression adds a new threat to the already observed decline of populations of O. hatcheri and suggests that this species deserves particular consideration in terms of conservation guidelines.