How do reproductive skew and founder group size affect genetic diversity in reintroduced populations?

Reduced genetic diversity can result in short-term decreases in fitness and reduced adaptive potential, which may lead to an increased extinction risk. Therefore, maintaining genetic variation is important for the short- and long-term success of reintroduced populations. Here, we evaluate how founder group size and variance in male reproductive success influence the long-term maintenance of genetic diversity after reintroduction. We used microsatellite data to quantify the loss of heterozygosity and allelic diversity in the founder groups from three reintroductions of tuatara ( Sphenodon ), the sole living representatives of the reptilian order Rhynchocephalia. We then estimated the maintenance of genetic diversity over 400 years (∼10 generations) using population viability analyses. Reproduction of tuatara is highly skewed, with as few as 30% of males mating across years. Predicted losses of heterozygosity over 10 generations were low (1–14%), and populations founded with more animals retained a greater proportion of the heterozygosity and allelic diversity of their source populations and founder groups. Greater male reproductive skew led to greater predicted losses of genetic diversity over 10 generations, but only accelerated the loss of genetic diversity at small population size (<250 animals). A reduction in reproductive skew at low density may facilitate the maintenance of genetic diversity in small reintroduced populations. If reproductive skew is high and density-independent, larger founder groups could be released to achieve genetic goals for management.     

Fine-scale genetic structure of a long-lived reptile reflects recent habitat modification

Anthropogenic habitat fragmentation — ubiquitous in modern ecosystems — has strong impacts on gene flow and genetic population structure. Reptiles may be particularly susceptible to the effects of fragmentation because of their extreme sensitivity to environmental conditions and limited dispersal. We investigate fine-scale spatial genetic structure, individual relatedness, and sex-biased dispersal in a large population of a long-lived reptile (tuatara, Sphenodon punctatus) on a recently fragmented island. We genotyped individuals from remnant forest, regenerating forest, and grassland pasture sites at seven microsatellite loci and found significant genetic structuring (R_ST = 0.012) across small distances (< 500 m). Isolation by distance was not evident, but rather, genetic distance was weakly correlated with habitat similarity. Only individuals in forest fragments were correctly assignable to their site of origin, and individual pairwise relatedness in one fragment was significantly higher than expected. We did not detect sex-biased dispersal, but natural dispersal patterns may be confounded by fragmentation. Assignment tests showed that reforestation appears to have provided refuges for tuatara from disturbed areas. Our results suggest that fine-scale genetic structuring is driven by recent habitat modification and compounded by the sedentary lifestyle of these long-lived reptiles. Extreme longevity, large population size, simple social structure and random dispersal are not strong enough to counteract the genetic structure caused by a sedentary lifestyle. We suspect that fine-scale spatial genetic structuring could occur in any sedentary species with limited dispersal, making them more susceptible to the effects of fragmentation.     

The loss of the lower temporal arcade in diapsid reptiles

The fossil record of diapsid reptiles does not provide conclusive evidence that the loss of the lower temporal arcade is correlated with the development of streptostyly. Analysis of the structure of the external jaw adductor in extant lizards results in the formulation of an alternative hypothesis to explain the loss of the lower temporal arcade in lepidosaurs. Extant lizards show the development of a posteroventral portion of the superficialis layer (lb) of the external adductor, which invades the lateral surface of the lower jaw, thus escaping the original confines of the external adductor. The development and expansion of a posteroventral lb muscle would have to be correlated with the loss of at least the posterior portion of the lower temporal arcade. Fossil lepidosaurs such as Clevosaurus, Prolacerta and Macrocnemus show the reduction of the lower temporal arcade from back to front, which is consistent with the hypothesis of the development of a posteroventral lb muscle.     

The functional diversity of epidermal keratins revealed by the partial rescue of the keratin 14 null phenotype by keratin 16.

The type I epidermal keratins K14 and K16 are remarkably similar at the primary sequence level. While a structural function has been clearly defined for K14, we have proposed that a function of K16 may be to play a role in the process of keratinocyte activation that occurs after acute injury to stratified epithelia. To compare directly the functions of the two keratins we have targeted the expression of the human K16 cDNA to the progenitor basal layer of the epidermis of K14 null mice. Mice null for K14 blister extensively and die approximately 2 d after birth (Lloyd, C., Q.C. Yu, J. Cheng, K. Turksen, L. Degenstein, E. Hutton, and E. Fuchs. 1995. J. Cell Biol. 129:1329-1344). The skin of mice expressing K16 in the absence of K14 developed normally without evidence of blistering. However, as the mice aged they featured extensive alopecia, chronic epidermal ulcers in areas of frequent physical contact, and alterations in other stratified epithelia. Mice expressing a control K16-C14 cDNA also rescue the blistering phenotype of the K14 null mice with only a small percentage exhibiting minor alopecia. While K16 is capable of rescuing the blistering, phenotypic complementation in the resulting skin is incomplete due to the multiple age dependent anomalies. Despite their high sequence similarity, K16 and K14 are not functionally equivalent in the epidermis and other stratified epithelia and it is primarily the carboxy-terminal approximately 105 amino acids of K16 that define these differences.     

Mark—Recapture Accurately Estimates Census for Tuatara,a Burrowing Reptile

Abstract: Estimates of population size are necessary for effective management of threatened and endangered species, but accurate estimation is often difficult when species are cryptic. We evaluated effectiveness of mark–recapture techniques using the Lincoln–Peterson estimator for predicting true census size of a population of tuatara (Sphenodon punctatus), a burrowing reptile that is a conservation priority in New Zealand. We found that Lincoln–Peterson estimates (NŇ = 85) were accurate for predicting the census size (N = 87) after only a 3-day mark–recapture survey. We recommend this method as a cost-effective way to accurately estimate population size for isolated, inaccessible tuatara populations, because it requires limited personnel, expertise, and time, and has low environmental impact on fragile sites.     

Complementary Roles of Specific Cysteines in Keratin 14 toward the Assembly,Organization, and Dynamics of Intermediate Filaments in Skin Keratinocytes

We recently showed that inter-keratin disulfide bonding plays an important role in the assembly, organization, and dynamics of keratin intermediate filaments in skin keratinocytes. In particular, cysteine 367 located in the central α-helical rod domain of keratin 14 is necessary for the formation of a stable perinuclear network of keratin filaments (with type II partner keratin 5) in skin keratinocytes analyzed by static and live cell imaging. Here, we show that two additional cysteine residues located in the non-helical head domain of K14, Cys-4 and Cys-40, also participate in inter-keratin disulfide bonding and tandemly play a key role complementary to that of Cys-367 in the assembly, organization, and dynamics of keratin filaments in skin keratinocytes in primary culture. Analysis of K14 variants with single or multiple substitutions of cysteine residues points to a spatial and temporal hierarchy in how Cys-4/Cys-40 and Cys-367 regulate keratin assembly in vitro and filament dynamics in live keratinocytes in culture. Our findings substantiate the importance and complexity of a novel determinant, namely inter-keratin disulfide bonding, for the regulation of several aspects of keratin filaments in surface epithelia.     

Lungs of the first amniotes: why simple if they can be complex?

We show—in contrast to the traditional textbook contention—that the first amniote lungs were complex, multichambered organs and that the single-chambered lungs of lizards and snakes represent a secondarily simplified rather than the plesiomorphic condition. We combine comparative anatomical and embryological data and show that shared structural principles of multichamberedness are recognizable in amniotes including all lepidosaurian taxa. Sequential intrapulmonary branching observed during early organogenesis becomes obscured during subsequent growth, resulting in a secondarily simplified, functionally single-chambered lung in lepidosaurian adults. Simplification of pulmonary structure maximized the size of the smallest air spaces and eliminated biophysically compelling surface tension problems that were associated with miniaturization evident among stem lepidosaurmorphs. The remaining amniotes, however, retained the multichambered lungs, which allowed both large surface area and high pulmonary compliance, thus initially providing a strong selective advantage for efficient respiration in terrestrial environments. Branched, multichambered lungs instead of simple, sac-like organs were part and parcel of the respiratory apparatus of the first amniotes and pivotal for their success on dry land, with the sky literally as the limit.