Population density and adult sex ratio of the tortoise Testudo hermanni in Greece: evidence for intrinsic population regulation

Sex Determination in Immature Sierra Nevada Lizard (Timon nevadensis)

Simple Summary

Sex determination in reptiles is frequently requested by reptile breeders, and it is a real challenge in reptiles with little or no sexual dimorphism, such as in immature subjects. Twenty-three clinically healthy young Sierra Nevada lizards (Timon nevadensis) aged between 4 and 6 months were included for sex determination using two techniques: cloacal probing and contrast radiography. Results showed that contrast radiography may have major sensitivity for sex determination compared to probing. Given the above, this technique could represent a valid and less invasive aid for sexing young lizards.

Abstract

Sex determination has a fundamental role in a captive breeding context, both for commercial reasons and in relation to animal welfare itself. However, this can be particularly difficult, especially in reptiles with little or no sexual dimorphism. Twenty-three clinically healthy young Sierra Nevada lizards (Timon nevadensis) were included in this study for sex determination. The first attempt at sexing was carried out by cloacal probing. A small, buttoned probe was inserted very gently into the hemipenal pouches, and the length of the inserted part was evaluated and measured. Subsequently, for each animal, a contrast medium was administered into the cloaca, and radiography was performed within 5 min. Through probing, 11 males and 8 females were recognized. The test was, however, equivocal in four subjects. In contrast radiography, 14 males and 9 females were identified. All the animals were rechecked after 8 months through an ultrasound examination, confirming 15 of the 14 previously male sexed animals based on contrast radiography. All the animals identified as female (n = 9) by contrast radiography were confirmed. From these results, it seems that contrast radiography may have major sensitivity in sex determination compared to probing. This technique could represent a valid and less invasive aid for sexing young lizards.

Salmonella Infection in Turtles: A Risk for Staff Involved in Wildlife Management?

Simple Summary

The aim of this study was to investigate the occurrence of non-typhoidal Salmonella in the turtles housed in a regional wildlife rescue centre of Apulia, in southern Italy, to assess the presence of Salmonella serovars that may represent a risk for operators involved in wildlife management. Sixty-nine tortoises, of which 36 were males and 33 were females, belonging to different species (Testudo hermanni hermanni, T. h. boettgeri, T. graeca, and T. marginata) were tested. All the turtles were adults (34 between 6 and 10 years of age and 35 more than 10 years of age). Salmonella was statistically detected more frequently in T. hermanni hermanni. No differences of the infection prevalence related to animal gender or age were found. Two different species, S. enterica and S. bongori, three S. enterica subspecies (enterica, diarizonae, salamae), and five different serovars (Hermannswerder, Abony, Ferruch, Richmond, Vancouver) within the group S. enterica subspecies enterica were identified. Two Salmonella types with different combinations were simultaneously found in specimens of T. h. hermanni. Most of the detected Salmonella types may represent a potential risk for operators in wildlife rescue centres.

Abstract

Monitoring of infections that may be transmitted to humans by animals in wildlife rescue centres is very important in order to protect the staff engaged in rehabilitation practices. Salmonella may be a natural inhabitant of the intestinal tract of turtles, rarely causing disease. This may represent a potential risk for humans, increasing the sanitary risk for operators in wildlife rescue centres. In this paper, the occurrence of non-typhoidal Salmonella among terrestrial turtles housed in a wildlife rescue centre in Southern Italy was investigated, in order to assess the serovars more frequently carried by turtles and identify those that may represent a risk for operators involved in wildlife management. Sixty-nine adult turtles (Testudo hermanni hermanni, T. h. boettgeri, T. graeca, and T. marginata) were tested. Detection and serotyping of Salmonella strains were performed according to ISO 6579-1 and ISO/TR 6579-3:2013, respectively. The distribution of Salmonella spp. was significantly higher in T. hermanni hermanni than in other species, independent of the age and gender of the animals. Two different Salmonella species, S. enterica and S. bongori, three S. enterica subspecies (enterica, diarizonae, salamae), and five different serovars (Hermannswerder, Abony, Ferruch, Richmond, Vancouver) within the group S. enterica subspecies enterica were identified. Different combinations of Salmonella types were simultaneously found in specimens of T. h. hermanni. Most of detected Salmonella types may represent a potential risk for public health. Adopting correct animal husbandry procedures and informing on potential sanitary risks may be useful for minimising the risk of transmission of Salmonella to workers involved in wildlife management.

Morphological Divergence of Hermann's Tortoise (Testudo hermanni boettgeri Mojsisovits, 1889) in Albania

Simple Summary

The morphology of chelonians provides basic information about development, evolution, biodiversity, biomechanics, behavior, ecology, and physiology. Furthermore, it has also played an important role in characterizing populations and analyzing the similarities between populations. This study investigates the morphological variation of Hermann’s tortoise (Testudo hermanni boettgeri Mojsisovits, 1889) between specimens from five different populations in Albania. It also provides basic data on the morphological characteristics of the Hermann’s tortoise. Hermann’s tortoise in the Albanian population were regionally diverged into three different populations that were situated in northern (Shkodra), central (Tirana, Berati, and Ballshi), and southern (Saranda) Albania. Moreover, female individuals were larger and heavier than male individuals, and the females followed Bergmann’s rule. The morphological divergences may be due to molecular variations or environmental conditions of the regions.

Abstract

Testudines show phenotypic plasticity, and variation among specific populations within a species is widespread. Morphological differences between populations may reflect ecological factors that drive adaptation to local conditions. In this context, we gathered basic data on the morphology of the Hermann’s tortoise (Testudo hermanni boettgeri Mojsisovits, 1889) to document their variation across different geographical regions. We surveyed Hermann’s tortoises in five different locales within Albania during April and May 2020 and measured 20 morphological characteristics, including carapace and plastron dimensions. We measured 188 tortoises (81 males, 107 females) in this study, and females were larger (p = 0.0001) and heavier (p = 0.0001) than males. Mean straight carapace length (SCL) and body mass were 172.4 mm and 1128.8 g, respectively, for females, and 151.3 mm and 735 g, respectively, for males. The Albanian T. h. boettgeri were regionally diverged into three different populations that were situated in northern (Shkodra), central (Tirana, Berati, and Ballshi), and southern (Saranda) Albania. The body size (curved carapace length (CCL)) of females was positively correlated (r = 0.216; p = 0.025) with the latitude, in accordance with Bergmann’s rule. However, there was no correlation between body size and latitude in males. These striking regional differences among Albanian T. h. boettgeri strongly suggest that further study of molecular variations and reproductive output of Hermann’s tortoises is warranted.

Male density, a signal for population self-regulation in Alligator sinensis

The regulation of population density is suggested to be indirect and occurs with a time-lag effect, as well as being female centred. Herein, we present a quantitative analysis on the precise, timely and male-dominated self-regulation of Chinese alligator (Alligator sinensis) populations. Analysis of 31 years of data revealed gender differences in regulation patterns. Population dynamics were restricted by male density rather than population density, and population growth was halted (birth rate = 0) when male density exceeded 83.14 individuals per hectare, until some males were removed, especially adult males. This rapid and accurate response supports the notions of intrinsic mechanisms and population-wide regulation response. Furthermore, density stress affected mating success rather than parental care to juveniles, i.e. females avoided unnecessary reproduction costs, which may represent an evolutionary advantage. Our findings highlighted the importance of further studies on related physiological mechanisms that focus on four characteristics: quantity breeds quality, gender differences, male density thresholds and nonlinearity.

Climate-driven shifts in adult sex ratios via sex reversals: the type of sex determination matters

Sex reversals whereby individuals of one genetic sex develop the phenotype of the opposite sex occur in ectothermic vertebrates with genetic sex-determination systems that are sensitive to extreme temperatures during sexual differentiation. Recent rises in global temperatures have led researchers to predict that sex reversals will become more common, resulting in the distortion of many populations' sex ratios. However, it is unclear whether susceptibility to climate-driven sex-ratio shifts depends on the type of sex determination that varies across species. First, we show here using individual-based theoretical models that XX/XY (male-heterogametic) and ZZ/ZW (female-heterogametic) sex-determination systems can respond differentially to temperature-induced sex reversals. Interestingly, the impacts of climate warming on adult sex ratio (ASR) depend on the effects of both genotypic and phenotypic sex on survival and reproduction. Second, we analyse the temporal changes of ASR in natural amphibian populations using data from the literature, and find that ASR shifted towards males in ZZ/ZW species over the past 60 years, but did not change significantly in XX/XY species. Our results highlight the fact that we need a better understanding of the interactions between genetic and environmental sex-determining mechanisms to predict the responses of ectotherms to climate change and the associated extinction risks.This article is part of the themed issue 'Adult sex ratios and reproductive decisions: a critical re-examination of sex differences in human and animal societies'.

Causes and consequences of adult sex ratio imbalance in a historical U.S. population

The responsiveness of individuals to partner availability has been well-documented across the literature. However, there is disagreement regarding the direction of the consequences of sex ratio imbalance. Specifically, does an excess of males or females promote male-male mating competition? In an attempt to clarify the role of the adult sex ratio (ASR) on behaviour, here we evaluate both competing and complimentary expectations derived from theory across the social and biological sciences. We use data drawn from a historical, nineteenth century population in North America and target several life-history traits thought to be affected by partner availability: age at first birth, relationship status, completed fertility and longevity. Furthermore, we assess the role of various contributors to a population's ASR. We find that both the contributors to and consequences of sex ratio imbalance vary over time. Our results largely support predictions of greater male pairbond commitment and lesser male mating effort, as well as elevated bargaining power of women in response to female scarcity. After reviewing our findings, and others from across the literature, we highlight the need to adjust predictions in response to ASR imbalance by the: (i) culturally mediated mating arena, (ii) variable role of demographic inputs across time and place, (iii) constraints to behavioural outcomes across populations, and (iv) ability and accuracy of individuals to assess partner availability.This article is part of the themed issue 'Adult sex ratios and reproductive strategies: a critical re-examination of sex differences in human and animal societies'.

Human-mediated secondary contact of two tortoise lineages results in sex-biased introgression

Human-mediated secondary contact of recently diverged taxa offers valuable opportunities for studying the evolutionary mechanisms involved in the establishment and maintenance of genetic boundaries between taxa. We used mitochondrial and microsatellite markers to examine a recently introduced population of the spur-thighed tortoise (Testudo graeca) of mixed origin in the Doñana National Park (SW Spain). The earliest records of tortoises in Doñana trace back to the 18th century, but several population reinforcements in the 20th century with animals from Morocco are well-documented. Consequently, different genetic lineages, which represent distinct subspecies, are thought to co-exist there. Our results confirmed the presence of distinct lineages by revealing that tortoises of the subspecies T. g. marokkensis were introduced into a local allochthonous T. g. graeca population. Unexpectedly, T. g. marokkensis haplotypes exclusively appeared in males, and admixture levels were statistically sex-biased toward males. The sex ratio of the population deviated from parity, with males being 2.36-fold more abundant than females. Our results indicated that population reinforcements had a strong effect on the genetic composition of this population and aggravated its sex ratio deviation. We predict that this sex-biased pattern of introgression is ephemeral and advocated to the near loss of T. g. marokkensis haplotypes.

Multiple paternity and sperm storage in captive Hermann's tortoises, Testudo hermanni boettgeri determined from amniotic fluid adhering to the eggshell

We identified multiple paternity in 52.9% of the clutches of Hermann's tortoise Testudo hermanni boettgeri using polymorphic microsatellite markers. In addition we demonstrated sperm storage across seasons. DNA was extracted from the amniotic fluid adhering to the eggshell's inner surface, a procedure suitable for easy, non-invasive DNA sampling in conservation and breeding programs. To improve the informative value of monomorphic single tandem repeat (STR) markers we additionally analyzed single nucleotide polymorphism (SNP) variability.

Status of the relict population of the Critically Endangered Madagascar spider tortoise Pyxis arachnoides

The Madagascar spider tortoise Pyxis arachnoides is endemic to the coastal dry forests of south-west Madagascar. In recent years its range has been reduced by c. 71%, with the species now confined to eight fragmented populations occupying a total of 2,464 km2. These remaining populations are facing a significant threat of extinction because of habitat destruction and other anthropogenic pressures. We developed methodology for a line transect distance sampling survey and applied it systematically across the species' range. The resulting distance model estimated a mean density of 226.9 tortoises km−2 (95% confidence interval, CI, 168.1–306.3) and a total population of 664,980 (95% CI 492,680–897,550). Fragmentation of the species’ range suggests the current population could be <30% of the historical population. Of the remaining population 73.5% falls within protected areas. However, nine of these 12 protected areas are designated as IUCN category III, V or VI parks, allowing some extractive activities to be undertaken. The most effective strategy for the conservation of P. arachnoides would be to reduce the threats to this species and its habitat, and to develop and expand the current community-based conservation and poverty alleviation programmes in the region.