185
7.3.6 Hybrids
Vilaça et al. (2012) analysed nuclear markers to investigate the pattern of hybridization involving three species of sea turtles: hawksbill (E. imbricata), loggerhead (C.
caretta) and olive ridley (L. olivacea). Results indicated that most of the individuals
in the crossings olive ridley x hawksbill and olive ridley x loggerhead are F1 hybrids,
whereas loggerhead x hawksbill crossings present F1 and backcrosses with both
parental species. It is a remarkable find, because most of the nesting sites surveyed
worldwide, including some in northern Brazil, presents no hybrids, and rare
Caribbean sites present no more than 2% of hybrids. Thus, a detailed understanding
of the hybridization process is needed to evaluate natural or anthropogenic causes
of this regional phenomenon, which could be an important factor affecting the conservation of the Brazilian population. Of special interest is the high occurrence of
loggerhead x hawksbill hybrids (42%), which display loggerhead mtDNA haplotypes but are characterized morphologically as hawksbills. The occurrence of several nesting individuals with identical mtDNA from another species may also
suggest a long history of introgression between species producing likely F2 or further generation hybrids (Vilaça et al. 2012).
7.4 Climate Change Impacts
Sea turtles will be affected by changes to multiple climatic processes (e.g., increased
air and sea temperature, sea level rise, precipitation, and storm activity) at all life
stages and at different temporal and geographical scales (Fuentes et al. 2011,
Hawkes et al. 2009). In addition, sea turtles will be affected indirectly by increased
atmospheric CO 2 concentrations and declines in ocean pH. Arguably, the more
detectable impacts of climate change to marine turtles will occur during their terrestrial reproductive phase (egg laying, egg incubation, and hatchling success)
because there are clear, and relatively straightforward, effects of increased temperature, sea level rise, and cyclonic activity on nesting sites and reproductive output
(Fuentes and Abbs 2010, Fuentes et al. 2009).
Successful incubation of sea turtle eggs occurs within a narrow thermal range of
25–33 °C. Incubation above the thermal threshold will result in hatchlings with
higher morphological abnormalities and lower hatching success. Additionally, all
species of sea turtle have temperature-dependent sex determination (TSD)
(Mrosovsky and Yntema 1980). Warmer temperatures, above the pivotal temperature—where a 1:1 sex ratio is produced—yield more females while temperatures
below the pivotal temperature shift the ratio towards more males. Consequently,
projected increases in temperature are expected to result in highly female-biased
populations, reduced hatching success and alteration of incubation duration (Fuentes
et al. 2011). Potential consequences include a reduction in effective population size,
the inability to find mates leading to reduced fecundity or female infertility, and
7 Novel Research Techniques Provide New Insights to the Sea Turtle Life Cycle
7.3.6 Hybrids
Vilaça et al. (2012) analysed nuclear markers to investigate the pattern of hybridization involving three species of sea turtles: hawksbill (E. imbricata), loggerhead (C.
caretta) and olive ridley (L. olivacea). Results indicated that most of the individuals
in the crossings olive ridley x hawksbill and olive ridley x loggerhead are F1 hybrids,
whereas loggerhead x hawksbill crossings present F1 and backcrosses with both
parental species. It is a remarkable find, because most of the nesting sites surveyed
worldwide, including some in northern Brazil, presents no hybrids, and rare
Caribbean sites present no more than 2% of hybrids. Thus, a detailed understanding
of the hybridization process is needed to evaluate natural or anthropogenic causes
of this regional phenomenon, which could be an important factor affecting the conservation of the Brazilian population. Of special interest is the high occurrence of
loggerhead x hawksbill hybrids (42%), which display loggerhead mtDNA haplotypes but are characterized morphologically as hawksbills. The occurrence of several nesting individuals with identical mtDNA from another species may also
suggest a long history of introgression between species producing likely F2 or further generation hybrids (Vilaça et al. 2012).
7.4 Climate Change Impacts
Sea turtles will be affected by changes to multiple climatic processes (e.g., increased
air and sea temperature, sea level rise, precipitation, and storm activity) at all life
stages and at different temporal and geographical scales (Fuentes et al. 2011,
Hawkes et al. 2009). In addition, sea turtles will be affected indirectly by increased
atmospheric CO 2 concentrations and declines in ocean pH. Arguably, the more
detectable impacts of climate change to marine turtles will occur during their terrestrial reproductive phase (egg laying, egg incubation, and hatchling success)
because there are clear, and relatively straightforward, effects of increased temperature, sea level rise, and cyclonic activity on nesting sites and reproductive output
(Fuentes and Abbs 2010, Fuentes et al. 2009).
Successful incubation of sea turtle eggs occurs within a narrow thermal range of
25–33 °C. Incubation above the thermal threshold will result in hatchlings with
higher morphological abnormalities and lower hatching success. Additionally, all
species of sea turtle have temperature-dependent sex determination (TSD)
(Mrosovsky and Yntema 1980). Warmer temperatures, above the pivotal temperature—where a 1:1 sex ratio is produced—yield more females while temperatures
below the pivotal temperature shift the ratio towards more males. Consequently,
projected increases in temperature are expected to result in highly female-biased
populations, reduced hatching success and alteration of incubation duration (Fuentes
et al. 2011). Potential consequences include a reduction in effective population size,
the inability to find mates leading to reduced fecundity or female infertility, and
7 Novel Research Techniques Provide New Insights to the Sea Turtle Life Cycle