Adult Female Turtles Research Articles

Bioaccumulation and impact of maternal PFAS offloading on egg biochemistry from wild-caught freshwater turtles (Emydura macquarii macquarii)

Per- and polyfluoroalkyl substances (PFAS) are persistent synthetic contaminants that are pervasive in the environment. Toxicity resulting from elevated PFAS concentrations in wildlife has been studied, yet evidence of their accumulation, developmental toxicity and maternal offloading in egg-laying species is limited. Here we show the maternal offloading of PFAS in freshwater short-necked turtles (Emydura macquarii macquarii) exposed to elevated PFAS and the resulting biological impact on oviducal eggs. Total PFAS concentrations were determined in serum from adult females and harvested oviducal eggs collected from euthanised turtles exposed to low and high levels of PFAS and compared against turtle serum and eggs collected from a suitable reference site. Multi-omics assays were utilised to explore the biochemical impact of elevated PFAS on egg albumen, yolk and eggshell using a range of metabolomics, lipidomics, and proteomics techniques. Eggshells were also screened for metals by Inductively Coupled Plasma Mass Spectrometry (ICP-MS). Analysis of the serum collected from adult female turtles and their oviducal eggs demonstrated PFAS offloading and transference that is 1.6 and 5.3 times higher in the low and high PFAS impacted eggs, respectively, compared to maternal serum concentrations. Oviducal egg yolk comprised >90% of the bioaccumulated PFAS load. Multi-omic analysis of the dissected egg fractions illustrated PFAS impacted eggs are significantly elevated in purine metabolism metabolites, which are tied to potential biological dysfunctional processes. The yolks were significantly depleted in lipids and lipid quality tied to growth and development. The high PFAS impacted oviducal eggshells were lower in calcium, important developmental and immune response proteins, and higher in glycerophosphoethanolamines (PE) lipids and histidine metabolism metabolites that are tied to a weakened physical structure. Further investigation is needed to establish the rate of PFAS offloading and quantify the developmental impact on hatchling and hatchling success to fully demonstrate PFAS-developmental toxicity linkages.

Fish-farming bolsters algal fouling and negatively affects condition and reproduction in European pond turtles (Emys orbicularis)

Fish-farming can lead to eutrophication of freshwater environments through the increase in organic matter resulting from food supplementation and fish wastes. Eutrophication can induce an excessive development of plants and algae on various substrates, including living organisms (algal epibiosis). Although algal epibiosis has been shown to reduce mobility by increasing drag in marine species, its consequences on host species in freshwater ecosystems remain poorly known. In this study, we investigated the individual (age and sex) and environmental (extensive versus intensive fish-farming) determinants of epizoic algae presence and abundance on European pond turtles (Emys orbicularis). We also explored the potential consequences of algal epibiosis on fitness-related traits of E. orbicularis. Based on a large sample size (1112 turtles from 23 ponds), we found that the abundance of algae growing on turtles increased during spring and summer. However, such increase was different across ages and sex; presumably reflecting the influence of thermoregulation (required to increase metabolic rates to sustain growth and reproduction) and thus, periodical drying of the shell, in reducing algal cover. We also found that intensive fish-farming increased algal epibiosis, especially when fish-farming involved food supplementation. Finally, we found that adult female body condition and reproduction of turtles were negatively linked to algal cover, thereby suggesting a potential negative impact of algal fouling on some fitness-related traits of adult female turtles. Future studies should usefully assess the demographic consequences of algal epibiosis induced by fish farming in this long-lived vertebrate.

Hormonal profile of Mediterranean green turtles (Chelonia mydas)

The beaches of Turkey are important nesting habitats of Chelonia mydas sea turtles and the determination of their health and disease status is critical in sustaining healthy populations. Limited data currently exist on the hormone values required to determine the status of reproductive capabilities of sea turtles. This study aimed to collect basic data regarding their hormonal profile and set reference limits for the Mediterranean population. Forty-nine free-ranging C. mydas sea turtles were used in the study and were classified into 3 groups according to their age (hatchlings, juvenile, adult). Adult turtles were also grouped according to sex. Adult females were further divided into 3 seasonal groups (summer, spring, and autumn), based on the dates of blood sampling. Plasma testosterone, oestradiol, progesterone, thyroxine (T4), triiodothyronine (T3), thyroid-stimulating hormone (TSH), cortisol, and corticosterone levels were determined by ELISA method. Significantly higher levels were observed in oestrogen (P < 0.001), progesterone (P < 0.001), cortisol (P < 0.05), corticosterone (P < 0.05), T3 (P < 0.05), and T4 (P < 0.01) in the adult turtles when compared with the other groups. The highest levels of oestrogen (280.2 ± 39.34), progesterone (274.2 ± 29.4), cortisol (2.26 ± 0.36), and corticosterone (2.94 ± 0.53) were determined in the adult female turtles during the spring season. This data could be used to protect the population of this endangered species by taking precautions against diseases via determining their blood hormone levels and taking precautions against reproductive diseases. Further work is required, but this research can expand the knowledge on the basic blood biochemistry of Mediterranean green turtles.

Depredation of gravid freshwater turtles by Raccoons (&lt;i&gt;Procyon lotor&lt;/i&gt;)

During summer 2017, we found 19 dead or fatally wounded adult female turtles belonging to three at-risk species at a nesting site on the north shore of Lake Erie, Ontario. Individuals were found flipped onto their carapace, had similar holes in their body cavities, and were eviscerated. Their eggs had also been consumed. Although turtle nest depredation by Raccoons (Procyon lotor) is common, it is unusual for them to target large numbers of gravid turtles within a season. Depredated species included Snapping Turtle (Chelydra serpentina), Northern Map Turtle (Graptemys geographica), and Blanding’s Turtle (Emydoidea blandingii). Our observation represents a spike in additive mortality for these populations, which could have long-term demographic consequences.

Identification of Important Sea Turtle Areas (ITAs) for hawksbill turtles in the Arabian Region

We present the first data on hawksbill turtle post-nesting migrations and behaviour in the Arabian region. Tracks from 90 post-nesting turtles (65 in the Gulf and 25 from Oman) revealed that hawksbills in the Arabian region may nest up to 6 times in a season with an average of 3 nests per turtle. Turtles from Qatar, Iran and the UAE generally migrated south and southwest to waters shared by the UAE and Qatar. A smaller number of turtles migrated northward towards Bahrain, Saudi Arabia and one reached Kuwait. Omani turtles migrated south towards Masirah island and to Quwayrah, staying close to the mainland and over the continental shelf. The widespread dispersal of hawksbill foraging grounds across the SW Gulf may limit habitat protection options available to managers, and we suggest these be linked to preservation of shallow water habitats and fishery management. In contrast, the two main foraging areas in Oman were small and could be candidates for protected area consideration. Critical migration bottlenecks were identified at the easternmost point of the Arabian Peninsula as turtles from Daymaniyat Islands migrate southward, and between Qatar and Bahrain. Overall, Gulf turtles spent 68% of the time in foraging ground with home ranges of 40–60km2 and small core areas of 6km2. Adult female turtles from Oman were significantly larger than Gulf turtles by ~11cm x¯=81.4CCL and spent 83% of their time foraging in smaller home ranges with even smaller core areas (~3km2), likely due to better habitat quality and food availability. Gulf turtles were among the smallest in the world x¯=70.3CCL and spent an average of 20% of time undertaking summer migration loops, a thermoregulatory response to avoid elevated sea surface temperatures, as the Gulf regularly experiences sustained sea surface temperatures >30°C. Fishery bycatch was determined for two of the 90 turtles. These spatio-temporal findings on habitat use will enable risk assessments for turtles in the face of multiple threats including oil and gas industries, urban and industrial development, fishery pressure, and shipping. They also improve our overall understanding of hawksbill habitat use and behaviour in the Arabian region, and will support sea turtle conservation-related policy decision-making at national and regional levels.

Assessment of Management Scenarios to Reduce Loggerhead Turtle Interactions with Shrimp Trawlers in Georgia

AbstractRecovery of loggerhead turtle Caretta caretta populations depends on many factors, including reducing anthropogenic mortality of adult turtles. Shrimp trawls are considered a major source of mortality for adult loggerhead turtles despite the mandatory use of turtle excluder devices. We modeled scenarios for reducing the likelihood of interaction between nesting adult loggerhead turtles and shrimp trawlers operating off the coast of Georgia during the nesting season (May–August). We used satellite telemetry and aerial surveys to describe the distribution patterns of nesting adult female turtles (2004–2005; n = 22) and shrimp trawls (1999–2005), respectively, across waters adjacent to the Georgia shoreline. Adult female turtles and shrimp trawlers both occupied state waters extensively during the nesting season. Turtles tended to have long, narrow home ranges that were located parallel to shore and that overlapped with the shrimp trawl distribution, which showed a slight grouping around deep channels. We modeled the efficacy of fleet reductions and spatial closures (accounting for fleet redistribution) in reducing shrimp trawler activity around loggerhead turtles. A comparison of spatial closures indicated that a large closure of state waters (∼200 km2) east of Sapelo and Blackbeard islands would reduce mean trawler activity levels in turtle home ranges. We also found that fleet reductions of 50% or more reduced potential interactions between turtles and trawlers. Although spatial closures produced a net total reduction in turtle–trawler interactions, fleet reductions yielded a reduction in such interactions across the study area. We recommend that to reduce loggerhead turtle–trawler interactions, state agencies should consider a limited‐entry system or some other means to limit the number of vessels operating within state waters.Received October 2, 2012; accepted July 17, 2013

Terrestrial habitat requirements of nesting freshwater turtles

Because particular life history traits affect species vulnerability to development pressures, cross-species summaries of life history traits are useful for generating management guidelines. Conservation of aquatic turtles, many members of which are regionally or globally imperiled, requires knowing the extent of upland habitat used for nesting. Therefore, we compiled distances that nests and gravid females had been observed from wetlands. Based on records of>8000 nests and gravid female records compiled for 31 species in the United States and Canada, the distances that encompass 95% of nests vary dramatically among genera and populations, from just 8m for Malaclemys to nearly 1400m for Trachemys. Widths of core areas to encompass varying fractions of nesting populations (based on mean maxima across all genera) were estimated as: 50% coverage=93m, 75%=154m, 90%=198m, 95%=232m, 100%=942m. Approximately 6–98m is required to encompass each consecutive 10% segment of a nesting population up to 90% coverage; thereafter, ca. 424m is required to encompass the remaining 10%. Many genera require modest terrestrial areas (<200m zones) for 95% nest coverage (Actinemys, Apalone, Chelydra, Chrysemys, Clemmys, Glyptemys, Graptemys, Macrochelys, Malaclemys, Pseudemys, Sternotherus), whereas other genera require larger zones (Deirochelys, Emydoidea, Kinosternon, Trachemys). Our results represent planning targets for conserving sufficient areas of uplands around wetlands to ensure protection of turtle nesting sites, migrating adult female turtles, and dispersing turtle hatchlings.

Home on the range: spatial ecology of loggerhead turtles in Atlantic waters of the USA

AbstractAim Although satellite tracking has yielded much information regarding the migrations and habitat use of threatened marine species, relatively little has been published about the environmental niche for loggerhead sea turtles Caretta caretta in north‐west Atlantic waters.Location North Carolina, South Carolina and Georgia, USA.Methods We tracked 68 adult female turtles between 1998 and 2008, one of the largest sample sizes to date, for 372.2 ± 210.4 days (mean ± SD).Results We identified two strategies: (1) ‘seasonal’ migrations between summer and winter coastal areas (n = 47), although some turtles made oceanic excursions (n = 4) and (2) occupation of more southerly ‘year‐round’ ranges (n = 18). Seasonal turtles occupied summer home ranges of 645.1 km2 (median, n = 42; using α‐hulls) predominantly north of 35 ° latitude and winter home ranges of 339.0 km2 (n = 24) in a relatively small area on the narrow shelf off North Carolina. We tracked some of these turtles through successive summer (n = 8) and winter (n = 3) seasons, showing inter‐annual home range repeatability to within 14.5 km of summer areas and 10.3 km of winter areas. For year‐round turtles, home ranges were 1889.9 km2. Turtles should be tracked for at least 80 days to reliably estimate the home range size in seasonal habitats. The equivalent minimum duration for ‘year‐round’ turtles is more complex to derive. We define an environmental envelope of the distribution of North American loggerhead turtles: warm waters (between 18.2 and 29.2 °C) on the coastal shelf (in depths of 3.0–89.0 m).Main conclusions Our findings show that adult female loggerhead turtles show predictable, repeatable home range behaviour and do not generally leave waters of the USA, nor the continental shelf (&lt; 200m depth). These data offer insights for future marine management, particularly if they were combined with those from the other management units in the USA.

Reproductive parameters in female yellow-blotched map turtles ( Graptemys flavimaculata) from a historically contaminated site vs. a reference site

Graptemys flavimaculata, the yellow-blotched map turtle, is a long-lived, threatened, species, endemic to the Pascagoula River drainage in Mississippi. During the 1980s, one branch of the drainage (i.e. the Leaf River) was impacted by effluent from a wood pulp processing plant known to contain endocrine disrupters. A decade later, we examined seasonal reproductive parameters (i.e. monthly plasma estradiol-17β (E 2), testosterone (T), vitellogenin (VTG) and follicular development) in adult female turtles from historically polluted and reference sites in the drainage to determine if legacy exposure to pollution impacts reproduction . We found no seasonal patterns in E 2 or T and these patterns did not differ between sites. However, E 2 differed significantly among ovarian stages for the reference, but not pollutant exposed females. A significantly greater percentage of reference site females were able to produce a second clutch than females from the historically polluted site (50% and 17%). Additionally, there was a significant positive correlation between E 2 with VTG levels for reference, but not pollutant exposed females. Body and yolk tissue contaminant analysis indicated that exposure to pollutants is presently minimal and unlikely the cause of the reproductive differences observed between sites; instead, differences are potentially due to exposure history.

Coelioscopic-assisted prefemoral oophorectomy in chelonians

To describe a coelioscopic-assisted prefemoral oophorectomy technique for use in chelonians. Descriptive report. 11 adult female turtles (6 red-eared sliders, 2 box turtles, 1 painted turtle, 1 four-eyed turtle, and 1 Chinese red-necked pond turtle). Five turtles required oophorectomy because of reproductive tract disease; the remaining 6 underwent elective oophorectomy. Turtles were anesthetized and positioned in dorsal recumbency. An incision was made in the prefemoral fossa, and a 2.7-mm rigid endoscope was inserted into the coelomic cavity and used to identify the ovaries. Each ovary was grasped with forceps and exteriorized through the prefemoral incision. The ovarian vasculature was ligated, and the mesovarium was transected. Closure was routine. In 8 turtles, bilateral oophorectomy was performed through a single incision. In 2 turtles, unilateral oophorectomy was performed in an attempt to maintain reproductive potential. In 1 turtle with a unilateral ovarian remnant from a previous surgery, unilateral oophorectomy was performed. Nine turtles recovered. One box turtle with severe hepatic lipidosis died 7 days after surgery. A second box turtle died 2 days after removal of retained eggs and a large bacterial granuloma. Results suggest that coelioscopic-assisted prefemoral oophorectomy is a practical and safe method for treating reproductive disorders and performing elective oophorectomy in turtles. This technique represents a potential alternative to plastron osteotomy in sexually mature chelonians.

Thyroid responses to altered photoperiod in the soft-shelled turtleLissemys punctata punctataBonnoterre

The aim of the current investigation was to investigate the effect of photoperiod on thyroid activity in soft-shelled turtles (Lissemys punctata punctata). Thirty days exposure of short photoperiod with 2L:22D increased relative weight, follicular epithelial height and peroxidase activity of the thyroid gland; whereas exposure of long photoperiod with 22L:2D for 30 days showed reversed changes to those of the short photoperiod in adult female turtles. These findings indicate that short photoperiod stimulates thyroid activity and long photoperiod inhibits its activity in soft-shelled turtles. It is suggested that photoperiod exerts its action on thyroid activity presumably via gonads and/or pineal-gonadal axis in turtles.

Connectivity in an Agricultural Landscape as Reflected by Interpond Movements of a Freshwater Turtle

Connectivity is a measure of how landscape features facilitate movement and thus is an important factor in species persistence in a fragmented landscape. The scarcity of empirical studies that directly quantify species movement and determine subsequent effects on population density have, however, limited the utility of connectivity measures in conservation planning. We undertook a 4-year study to calculate connectivity based on observed movement rates and movement probabilities for five age-sex classes of painted turtles (Chrysemys picta) inhabiting a pond complex in an agricultural landscape in northern Virginia (U.S.A.). We determined which variables influenced connectivity and the relationship between connectivity and subpopulation density. Interpatch distance and quality of habitat patches influenced connectivity but characteristics of the intervening matrix did not. Adult female turtles were more influenced by the habitat quality of recipient ponds than other age-sex classes. The importance of connectivity on spatial population dynamics was most apparent during a drought. Population density and connectivity were low for one pond in a wet year but dramatically increased as other ponds dried. Connectivity is an important component of species persistence in a heterogeneous landscape and is strongly dependent on the movement behavior of the species. Connectivity may reflect active selection or avoidance of particular habitat patches. The influence of habitat quality on connectivity has often been ignored, but our findings highlight its importance. Conservation planners seeking to incorporate connectivity measures into reserve design should not ignore behavior in favor of purely structural estimates of connectivity.

The effect of sex-specific terrestrial movements and roads on the sex ratio of freshwater turtles

Differential road mortality may affect the demography of vertebrate populations when movements associated with foraging, reproduction, or dispersal cause a greater proportion of one sex or stage to frequently contact roads. In the case of turtles, roadsides create artificial disturbed and open habitats that may be attractive to nesting females but may cause significant road mortality. I tested this possibility by comparing the sex ratios of turtle populations in a lake that is bisected by a high-traffic, four-lane highway to those in nearby ponds located away from major roads in northwestern Florida (USA). I evaluated the potential role of road mortality as the cause of skewed sex ratios by determining whether adult female freshwater turtles move overland more frequently than that expected from actual sex ratios and the proportions of turtles of four species that attempt to nest annually along the roadside. Population sex ratios were dramatically biased toward males in the Florida cooter ( Pseudemys floridana) (80% males), yellow-bellied slider ( Trachemys scripta) (73% males), and common musk turtle ( Sternotherus odoratus) (65% males) in the lake adjacent to the highway compared to those in ponds not affected by road mortality, where the proportion of males ranged from 39% to 60%. Despite male-biased population sex ratios, under normal (non-drought) conditions a significantly greater proportion of adult females (57–72%) than males were found on land along the highway and, thus, have a greater annual probability of being killed by vehicles. An estimated 6–29% of all adult females in four turtle species nested annually along the highway shoulder. If this phenomenon is general for freshwater turtle populations located near roadways, male-biased sex ratios and low numbers of adult female turtles elsewhere may be the result of cumulative differential mortality of nesting females struck by vehicles as they enter the highway during annual nesting forays.

Ultrastructural changes in granulosa cells and plasma steroid levels after administration of luteinizing hormone-releasing hormone in the Western painted turtle, Chrysemys picta

In this study we investigated the effects of treatment by luteinizing hormone-releasing hormone (LHRH) on the morphology and steroid release of ovarian tissues in the Western painted turtle, (Chrysemys picta). In Experiment I, four adult female turtles were injected with synthetic mammalian LHRH (i.p., 500pg/g bodyweight) and four with saline 2–3 weeks prior to ovulation. Granulosa cells from LHRH-treated turtles vs controls contained both preovulatory follicles (16–20mm in diameter) and small follicles (0.5–1.00mm in diameter) with increased RER, free ribosomes and mitochondria with swollen cristae. An increase in the amount of cytoskeletal material (microfilaments) was observed in granulosa cells of the experimental turtles compared to the controls. Cytoplasmic extensions of the oocyte and granulosa cells were longer in the small follicles of treated animals, accounting for the observed increase in the thickness of the zona pellucida (ZP) over the controls. In Experiment II, administration of LHRH (i.p.) to 10 turtles during the same period triggered a substantial increase in plasma progesterone and estradiol-17β levels over the 10 saline-injected controls. This supports the idea that in this species, as in mammals, steroidogenic activity in the ovarian follicles are under the control of the hypothalamic–pituitary axis. The ultrastructure and hormonal levels of the experimental animals were typical of untreated turtles just prior to ovulation. In this species the development of follicles and steroidogenesis can be stimulated prematurely by a releasing hormone from a nonreptilian origin.

Evidence for a Hormonal Tactic Maximizing Green Turtle Reproduction in Response to a Pervasive Ecological Stressor

Mortality of breeding sea turtles due to excessive heat exposure after nesting activities is an unusual feature of the Raine Island green turtle rookery. Breeding turtles that fail to return to the ocean after oviposition can experience increasing body temperatures that exceed lethal limits (>39°C) as ambient temperatures rise after sunrise. We investigated how acute increases in body temperature influenced plasma corticosterone (B) concentrations of individual turtles. Furthermore, interactions between progesterone (P) and testosterone (T) and increasing body temperature and the glucocorticoid corticosterone were examined for negative correlations. Breeding green turtles exhibited a 16-fold mean increase in plasma corticosterone concentration as body temperature (cloacal) rose from 28.2 to 40.7°C in less than 6 h. However, the absolute increase in plasma B was small and much less than expected, despite the lethal stressor. Comparatively, the maximal B response to lethal heat stress was similar to plasma B concentrations obtained from breeding female turtles exposed to 8 h of capture stress. However, the maximal B response of breeding turtles exposed to heat and capture stressors was significantly less than the B response of nonbreeding adult female turtles subjected to an 8-h capture stressor. No negative correlations were observed between plasma T and plasma B, between plasma T and body temperature, between plasma P and plasma B, or between plasma P and body temperature. Our findings provide further evidence that reduced adrenocortical function operates in breeding green turtles in the presence of even the most pervasive of environmental stressors.

Fat reserves and reproduction in the green turtle, Chelonia mydas

Measurements were made of the fat and water content of standard cores of fat lining the inner carapace of green turtles caught and butchered by indigenous fishermen in Daru, Papua New Guinea. The amount of depot fat, total lipid and neutral lipid per core varied with the sex, maturity and reproductive status of the turtle. The fat content of cores from prepubescent turtles did not vary with sex. In contrast, cores from adult female turtles had a significantly greater fat content than those from males. Cores from pubescent and vitellogenic females had the highest fat content. Neutral (storage) lipid was significantly higher in cores from vitellogenic females than in those from breeding, which suggests that sub-carapace depot fat is used to fuel the energetically expensive costs of migration and egg production. Cores from breeding females had a significantly higher fat content than those from males, which suggests that the energetic costs of vitellogensis and egg-laying are reflected in sub-carapace fat stores. The greater energetic cost to this fat store for breeding by females is also reflected in the significantly higher water content of the fat of females that had bred in the previous season compared with those in vitellogenesis. In contrast, there was no significant difference between the water content of cores from non-breeding and breeding males.

Organic contaminants in snapping turtle (Chelydra serpentina) populations from southern Ontario, Canada

Organochlorine contaminant levels were measured in 78 adult snapping turtles collected from 16 sites in southern Ontario, Canada in 1988/89 to evaluate the risk to humans of consuming snapping turtles. Significant differences in turtle contaminant levels were observed among sites. Mean levels in muscle, at all sites, were below fish consumption guidelines for total polychlorobiphenyls (PCBs), total DDT and mirex. However, contaminant levels in older turtles from some sites exceeded guideline values. Multivariate statistical techniques indicated the existence of a highly significant relationship between contaminant levels in adult female turtles and their eggs. Multivariate techniques also identified differences in contaminant composition in adult snapping turtles from sites in the Great Lakes where differences in reproductive success have been previously observed. The mono-ortho substituted PCB congener 2,3,4,3′,4′-pentachlorobiphenyl (IUPAC #105) may be an important contributor to the toxic burden of snapping turtle populations.

Behavioural studies on the green turtle ( Chelonia mydas) in the sea

Underwater observations of green turtles near Fairfax Island, Bunker Group, Australia, disclosed female behaviour patterns to avoid copulation, including a striking adpressed hind limb position; resting in a female sanctuary area; avoidance swimming; face-to-face confrontation, followed or accompanied by biting; and a ‘refusal’ position, with the female assuming a vertical position, her limbs widely outspread and plastron facing the male. Copulation activity precedes egg laying on Fairfax. Copulation lasts as long as 6 hr. Females outnumber males, who engage in multiple copulations. The ‘escort’ is a group of one to five males attendant upon mated pairs. Hatchlings feed on various invertebrates. Cleaner fishes groom adult female turtles.

Sexual and Relative Growth Differences in Brain Regions of the Turtle Pseudemys scripta (Schoepff)

Weights of nine individually dissected brain regions were determined from 32 specimens of Pseudemys scripta obtained commercially from Louisiana. Four size classes were represented. Within adult size classes weights of brain regions were significantly greater in males than in females of similar body weight or carapace length. This sexual difference was greatest with the cerebral weight and least or lacking with the tectal and cerebellar weights. This difference may originate from the known slower growth rate of body and shell in adult male as compared with adult female turtles. However, males and females showed similar growth trends in the proportional representations between weights of particular brain regions and weight of whole brain from post-hatching to adult sizes.

The role of vision in the sea-finding orientation of the green turtle ( Chelonia mydas)

Summary Two tests of sea-finding orientation were used to determine the nature of the visual cues that guide green turtles to the sea after hatching or nesting. The orientation performance, in day-light, during 143 trials with adult female turtles was evaluated quantitatively while they were wearing spectacles containing different filters; and a total of 525 hatchlings was tested at various times of day and night in a circular arena near the sea, where direction preferences might be observed when the view of the horizon was unobstructed, or when it was blocked by a low wall. Blindfolded turtles were unable to find the sea except by chance; their performance was worse than that of any other group. Red, blue, and 0·4 neutral density filters significantly decreased orientation scores. Turtles with green filters, and those with neutral density filters and depolarizing-diffusing filters to which the animals had been pre-adapted, were able to orient as well as control animals with clear filters. Hatchlings placed in the low-walled arena headed in a landward direction nearly 50 per cent of the time despite a clear view of the sky. Sea-finding orientation was highly successful in the unwalled arena during both day and night, although there was no direct view of the sea. Theere was little correlation between hatchling direction preferences and the pattern of light intensity in the sky above the horizon, as measured by a photometer. Some conclusions based upon these results are as follows: o 1. Sea-finding orientation is primarily a visual process. 2. There was no evidence of an ‘innate’ compass direction preference based on celestial information. 3. A direct view of the sea or surf is not necessary for seaward orientation of either adults or hatchlings. 4. Light polarized by reflection from the surface of the sea is not used as a primary orienting stimulus when the water, itself, is not in sight. 5. Orientation is not impaired when the details of visual images are blurred by a diffusing filter. 6. It is unlikely that true colour preference forms the behavioural basis of the sea-finding guidance system. The results of the spectacle experiments with colour filters may be interpreted to mean that marine turtles are less sensitive to red light than are fresh-water turtles. 7. The principal sea-finding process is visual inspection of the beach horizon and landscape features. It is not clear whether an avoidance of dark areas or an attraction to open, brighter portions of the beach is involved; the two may co-exist, and further studies are necessary to resolve the problem. A comparison of our results with those of previous studies suggests that fresh water and marine turtles have solved the problem of water-finding in the same way.