Macroecological patterns of sexual size dimorphism in turtles of the world.

Sexual size dimorphism (SSD) is a well-documented phenomenon in both plants and animals; however, the ecological and evolutionary mechanisms that drive and maintain SSD patterns across geographic space at regional and global scales are understudied, especially for reptiles. Our goal was to examine geographic variation of turtle SSD and to explore ecological and environmental correlates using phylogenetic comparative methods. We use published body size data on 135 species from nine turtle families to examine how geographic patterns and the evolution of SSD are influenced by habitat specialization, climate (annual mean temperature and annual precipitation) and climate variability, latitude, or a combination of these predictor variables. We found that geographic variation, magnitude and direction of turtle SSD are best explained by habitat association, annual temperature variance and annual precipitation. Use of semi-aquatic and terrestrial habitats was associated with male-biased SSD, whereas use of aquatic habitat was associated with female-biased SSD. Our results also suggest that greater temperature variability is associated with female-biased SSD. In contrast, wetter climates are associated with male-biased SSD compared with arid climates that are associated with female-biased SSD. We also show support for a global latitudinal trend in SSD, with females being larger than males towards the poles, especially in the families Emydidae and Geoemydidae. Estimates of phylogenetic signal for both SSD and habitat type indicate that closely related species occupy similar habitats and exhibit similar direction and magnitude of SSD. These global patterns of SSD may arise from sex-specific reproductive behaviour, fecundity and sex-specific responses to environmental factors that differ among habitats and vary systematically across latitude. Thus, this study adds to our current understanding that while SSD can vary dramatically across and within turtle species under phylogenetic constraints, it may be driven, maintained and exaggerated by habitat type, climate and geographic location.

Prevalence and histopathology of shell disease in turtles from Lake Blackshear, Georgia.

Turtles in Lake Blackshear, Crisp County, Georgia (USA) were evaluated for shell disease during intensive trapping efforts on 8 and 9 May 1990. The disease was most prevalent in Pseudemys concinna (74%) and Trachemys scripta (35%). The degree of necrosis on the carapace was significantly positively correlated with the degree of necrosis on the plastron in T. scripta (rs = 0.50), but not in P. concinna (rs = 0.06). Female T. scripta with lesions were significantly larger than females without lesions. Lesions were not detected on six other species of turtles. Some areas contained multinucleate osteoclasts that were destroying bone. No tumors were detected in soft tissue samples.

A review of techniques for quantifying sexual size dimorphism.

Previous studies of sexual size dimorphism (SSD) use a variety of size dimorphism indices (SDI's) to quantify SSD. We propose that a useful SDI should meet four criteria as follows; 1) it should be properly scaled, 2) it should have high intuitive value, 3) it should produce values with one sign, (positive) when sex A is larger than sex B, and the opposite sign when sex B is larger, and 4) it should produce values that are symmetric around a central value, preferably zero. Many previously published SDI's do not meet any of these criteria, and none meet more than three. We present an alternative SDI based on the mean size of the larger sex divided by the mean size of the smaller sex with the result arbitrarily defined as positive (minus one) when females are larger and negative (plus one) in the converse case. Careful selection of a primary size variable is crucial to meaningful interpretation of sexual size differences.

Nursing supports neonatal porcine testicular development.

The lactocrine hypothesis suggests a mechanism whereby milk-borne bioactive factors delivered to nursing offspring affect development of neonatal tissues. The objective of this study was to assess whether nursing affects testicular development in neonatal boars as reflected by: (1) Sertoli cell number and proliferation measured by GATA-4 expression and proliferating cell nuclear antigen immunostaining patterns; (2) Leydig cell development and steroidogenic activity as reflected by insulin-like factor 3 (INSL3), and P450 side chain cleavage (scc) enzyme expression; and (3) expression of estrogen receptor-alpha (ESR1), vascular endothelial growth factor (VEGF) A, and relaxin family peptide receptor (RXFP) 1. At birth, boars were randomly assigned (n = 6-7/group) to nurse ad libitum or to be pan fed porcine milk replacer for 48 h. Testes were collected from boars at birth, before nursing and from nursed and replacer-fed boars at 50 h on postnatal day (PND) 2. Sertoli cell proliferating cell nuclear antigen labeling index increased (P < 0.01) from birth to PND 2 in nursed, but not in replacer-fed boars. Sertoli cell number and testicular GATA-4 protein levels increased (P < 0.01) from PND 0 to PND 2 only in nursed boars. Neither age nor nursing affected testicular INSL3, P450scc, ESR1, or VEGFA levels. However, testicular relaxin family peptide receptor 1 (RXFP1) levels increased (P < 0.01) with age and were greater in replacer-fed boars on PND 2. Results suggest that nursing supports neonatal porcine testicular development and provide additional evidence for the importance of lactocrine signaling in pigs.