Sex allocation and secondary sex ratio in Cuban boa (Chilabothrus angulifer): mother's body size affects the ratio between sons and daughters.

Secondary sex ratios of animals with genetically determined sex may considerably deviate from equality. These deviations may be attributed to several proximate and ultimate factors. Sex ratio theory explains some of them as strategic decisions of mothers improving their fitness by selective investment in sons or daughters, e.g. local resource competition hypothesis (LRC) suggests that philopatric females tend to produce litters with male-biased sex ratios to avoid future competition with their daughters. Until now, only little attention has been paid to examine predictions of sex ratio theory in snakes possessing genetic sex determination and exhibiting large variance in allocation of maternal investment. Cuban boa is an endemic viviparous snake producing large-bodied newborns (∼200 g). Extremely high maternal investment in each offspring increases importance of sex allocation. In a captive colony, we collected breeding records of 42 mothers, 62 litters and 306 newborns and examined secondary sex ratios (SR) and sexual size dimorphism (SSD) of newborns. None of the examined morphometric traits of neonates appeared sexually dimorphic. The sex ratio was slightly male biased (174 males versus 132 females) and litter sex ratio significantly decreased with female snout-vent length. We interpret this relationship as an additional support for LRC as competition between mothers and daughters increases with similarity of body sizes between competing snakes.

Strong support for Rensch's rule in an American clade of lizards (Teiidae and Gymnophtalmidae) and a paradox of the largest tejus.

Rensch's rule predicts an allometric relationship between male and female body size stating that the sexual size dimorphism (SSD) increases with body size in male-larger taxa and decreases in female-larger taxa in groups of related species. It means that the relationship between the male and female body size is hyperallometric, i.e., the allometric exponent of this relationship exceeds the unity. We explored the relationship between the male and female body size in a New World clade of lizards consisting of sister families Teiidae and Gymnophthalmidae, which exhibit a great variation in both their adult body sizes and SSD. All our estimates of the reduced major axis regression slopes ranged from 1.067 to 1.229 and clearly followed a pattern consistent with the Rensch's rule. Despite a clear general trend, giant species from the subfamily Tupinambinae show paradoxically only poor SSD. The cases of extreme male-larger SSD were found in species of moderate body size belonging to the genera Ameiva and Cnemidophorus. The abovementioned deviations from the hyperallometric relationship between the male and female body size are surprising and require further examination.

Mitochondrial DNA variation reveals recent evolutionary history of main Boa constrictor clades.

We sequenced a 1114-bp fragment of cytochrome b gene in six subspecies (115 samples) of Boa constrictor and detected 67 haplotypes. Our analyses revealed the presence of two distinct clades, one from Central America (CA) including the neighboring part of South America west of the Andes, and the other covering the rest of South America (SA). Sequence divergence between CA and SA clades is about 5-7%, which roughly corresponds to a separation at the time of uplift of the Colombian Andes following formation of the Panama Isthmus before 3.5 Myr Sequence divergence within the SA and CA clades is only 2-3%, suggesting a fairly recent spread of these clades Into their current geographic ranges. Thus, we may not be dealing with taxa with a markedly old evolutionary history. Because juveniles of B. constrictor feed mostly on small rodents, we hypothesized that spread of this species was allowed by a new food source represented by murold rodents that appeared after closure of the Panama portal. With respect to the taxonomy, B. c. imperator may be elevated to full species rank. Within the SA clade, a haplotype of Argentinian B. c. occidentalis is markedly distinct, while the remaining haplotype groups analyzed are distributed throughout large ranges and may all belong to a single nominotypic subspecies.