engleski

Histology of gonads and preliminary sex ratios in juvenile loggerhead sea turtles, Caretta caretta, in the eastern Adriatic Sea

Sexes of 30 and 32 juvenile loggerhead sea turtles (Caretta caretta) with CCL ranging from 25.0-70.0 cm (mean CCL = 41.3, SD: 10.6) were determined by a visual examination of gonads and histological analysis, respectively. Ovaries exhibited membranous structures, folded, often partly transparent, enclosing spherical follicles. The stromatic tissue was abundant in the medullar region, while columnar, multistrafied epithelium of the cortex contained germ cells. Testes were light-coloured, elongated and solid with a relatively uniform texture formed of the seminiferous cords with germ cells and abundant stromal tissue. Visual examination of gonads resulted in sex ratio of 1:1, while histology gave a slightly male-biased sex ratio (1.66), but not significantly different from a 1:1 ratio (chi-square = 2.00, p = 1.157, df =1). A recent comparison of testosterone levels and mtDNA haplotypes in loggerheads from central Mediterranean indicated a male-biased dispersal of northwestern Atlantic pelagic juveniles into Mediterranean. Such difference in migratory behavior between male and female juveniles is larger for specimens further from their natal areas, and consists in a stronger male-bias. If we consider that about 50% of pelagic juveniles in the Mediterranean originate from northwestern Atlantic populations, most of them being males, we can expect that in shared habitats male-skewed immigration would buffer the original female-bias of the Mediterranean pelagic juvenile populations. That seems to be the case in the Adriatic, which probably hosts developmental habitats for loggerheads belonging to both Mediterranean and NW Atlantic populations. Considering the assumed higher reproductive value of females, human impact, such as fishery, would affect more populations from closer nesting sites than the distant ones. If the sex-biased dispersal happens already in the pelagic juvenile phase, high by-catch level in Adriatic fisheries would have the most detrimental effect for loggerheads from the regional nesting grounds.

sex ratios; gonadal development; marine habitats; nesting beaches; migrations; Mediterranean

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