Abstract
There is increasing concern about feminization of sea turtle populations resulting from female-biased production of hatchlings due to climate change and selective loss of males from other anthropogenic drivers. Extreme female-biased breeding populations would reduce the likelihood of successful mating and potentially result in high rates of infertile eggs. Infertile eggs are those in which none of the events between sperm penetration of the ovum and syngamy have occurred. Distinguishing between fertile and infertile eggs is challenging, especially in field conditions, and researchers often have relied on physical evidence gathered from unhatched eggs at the end of the incubation period, which likely have experienced tissue decomposition. We argue that infertility in sea turtle eggs can be demonstrated only by the absence of holes caused by sperm penetration of the inner perivitelline membrane; sperm bound between the inner and outer perivitelline membranes; nuclei in the blastodisc; embryonic tissue or membranes in egg contents; and/or the characteristic white spot on the egg exterior. Unhatched eggs can be examined at the end of the incubation period, but we recommend that studies specifically investigating infertility examine at least 20 oviposited eggs each from clutches laid by at least 20 different turtles at the peak of the nesting season.
Highlights
The number of live hatchlings produced from sea turtle eggs is commonly recorded by most sea turtle nesting beach monitoring projects and used to estimate hatching success of a clutch, defined as the number of hatchlings produced, divided by the number of yolked eggs deposited (Miller 1999)
Examination of dead embryos found within unhatched eggs that remain in the nest cavity after the live
In earlier publications of sea turtle biology and development and tissue had decomposed by the time management, unhatched eggs without visible signs failed eggs are examined at hatchling emergence of embryonic development were categorized as infer- (Blanck & Sawyer 1981, Wyneken et al 1988, Bell et tile (e.g. Ragotzkie 1959, Balasingam 1967, Hughes & al. 2004)
Summary
The number of live hatchlings produced from sea turtle eggs is commonly recorded by most sea turtle nesting beach monitoring projects and used to estimate hatching success of a clutch, defined as the number of hatchlings produced, divided by the number of yolked eggs deposited (Miller 1999). Williamson et al (2017b) Olive ridley 303 eggs from 6 clutches tile if embryonic mortality occurred early in Phillott & Godfrey: Assessing infertility in sea turtle eggs proximately Day 9 after ovulation) until oviposition (Miller 1985) This arrest is maintained by hypoxic conditions in the oviduct (Rafferty et al 2013). Intra-oviducal embryonic mortality can occur during gastrulation or developmental arrest, and potentially at higher rates if eggs are retained in the oviduct during a long inter-clutch interval (Rafferty et al 2011, Booth & Dunstan 2018; and see Rings et al 2015, Williamson et al 2019) Embryos at this time are developed to Stages 1−6 (Miller 1985) and < 2 mm in length (Miller 1985, Miller et al 2017). Post-ovipositional early embryonic mortality, due to unsuitable temperature, moisture, or respiratory gas availability in the nest environment (Ragotzkie 1959, Foley et al 2006, Howard et al 2014, Bézy et al 2015) or inappropriate movement while handling during sensitive periods (Limpus et al 1979, Parmenter 1980, Chan et al 1985), may be difficult to discern before signs of embryonic development become visible to the unaided eye at approximately Stages 13−16 and an embryo length of ~10 mm (Days 4−9 after oviposition) (Leslie et al 1996, Ralph et al 2005)
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