The microscopic anatomy of epidermal glands in two species of gekkonine lizards, with some observations on testicular activity.

The gross and microscopic anatomy of epidermal glands has been studied in laboratory maintained tokays (Gekko gecko), and house geckos (Hemidactylus bowringii) captured from the wild throughout the year. Annual testicular activity in the house gecko has also been studied. While no significant differences in glandular development at various times have been observed in G. gecko, there are clear-cut annual cycles in H. bowringii. The evolution of epidermal glands in gekkonid lizards is reviewed; the cellular dynamics of beta-glands are compared with those of unspecialized epidermis; the possibility that gekkonine epidermal glands respond to quantitative variation in circulating testosterone titers is discussed.     

Sex chromosome evolution in reptiles: divergence between two lizards long regarded as sister species,Lacerta vivipara andLacerta andreanskyi

Even if the common lizardLacerta vivipara and endemicLacerta andreanskyi from Moroccan Grand Atlas have the same mother species, the two species are definitely not closely related in present-day nature, whereL. vivipara stands at variance from all other lacertids in terms of cytogenetics. The use of replication banding, C-bands and R-bands has allowed for the identification of all chromosome pairs and two sex chromosomes inL. andreanskyi. Its karyotype is typical of Lacertidae. The W chromosome, characterized by late replication, is nevertheless of a type previously unknown in the family. The comparison of Z and W chromosomes by different methods of chromosome banding indicates little homology between them, if any. The replication study has shown that there is no dosage compensation for the Z chromosome in (homogametic) males. That genetic inactivation precedes chromosomal mutations in non-vivipara lacertid evolution of the odd sex chromosome is suggested.     

The post-natal development of holocrine epidermal specializations in gekkonid lizards.

The abdominal escutcheon, and certain aspects of pre-anal organ morphology, have been studied in Sphaerodactylus spp. and Gekko vittatus respectively. These epidermal modifications are male characteristics. The sphaerodactyline escutcheon becomes larger by the peripheral addition of specialized scales with increasing size of the individuals: this relationship is much more clearcut in S. cinereus than in the notatus species group (sensu Shreves, '68), and the possible reasons for this are discussed. The number of pre-anal organs varies between populations of G. vittatus, but within populations remains constant throughout life. Individual organs increase steadily in size throughout life. These data are discussed with reference to current interpretations of gekkonid gland evolution, and of factors controlling epidermal cell proliferation and differentiation.     

The relevance of morphology for habitat use and locomotion in two species of wall lizards

Understanding if morphological differences between organisms that occupy different environments are associated to differences in functional performance can suggest a functional link between environmental and morphological variation. In this study we examined three components of the ecomorphological paradigm – morphology, locomotor performance and habitat use – using two syntopic wall lizards endemic to the Iberian Peninsula as a case study to establish whether morphological variation is associated with habitat use and determine the potential relevance of locomotor performance for such an association. Differences in habitat use between both lizards matched patterns of morphological variation. Indeed, individuals of Podarcis guadarramae lusitanicus, which are more flattened, used more rocky environments, whereas Podarcis bocagei, which have higher heads, used more vegetation than rocks. These patterns translated into a significant association between morphology and habitat use. Nevertheless, the two species were only differentiated in some of the functional traits quantified, and locomotor performance did not exhibit an association with morphological traits. Our results suggest that the link between morphology and habitat use is mediated by refuge use, rather than locomotor performance, in this system, and advise caution when extrapolating morphology-performance-environment associations across organisms.     

Effect of testosterone on T cell-mediated immunity in two species of Mediterranean lacertid lizards

One of the primary assumptions of the immunocompetence handicap hypothesis is that testosterone has an immunosuppressive effect, but conflicting results have been reported in a variety of bird species concerning the effect of testosterone on the humoral and the T cell-mediated components of the immune system. The T cell-mediated component of the immune system is particularly important during the breeding season, because the likelihood of injury during sexual competition is high and T cell-mediated immunity is essential for healing wounds and resisting infection. In this study we examined the effect of experimentally increased levels of testosterone during breeding season on T cell-mediated immunity in male lizards of two Mediterranean lacertid species, Psammodromus algirus and Acanthodactylus erythrurus. The hormonal treatment significantly increased testosterone of the experimental individuals. T cell-mediated responses to phytohemagglutinin stimulation were significantly suppressed in testosterone-treated males of both species. Furthermore, there was a significant negative relationship between individual variability in T cell-mediated responsiveness and plasma testosterone concentration. The present study is the first to demonstrate testosterone-induced suppression of T cell-mediated immunity in lizards.     

The epidermal glands of Nereis

Summary Three types of unicellular glands have been identified from the parapodial epithelium of Nereis. They conform to a common plan. The cell body, which lies at the base of the epithelium, has prominent rough-faced endoplasmic reticulum and golgi. It sends a long intra-cellular duct to the cuticle where it opens through a pore lined by the epicuticle. The end of the duct in two of the glands bears a ring of microvilli. The duct of the type-6 gland is lined by cytoplasm containing elongated mitochondria and endoplasmic reticulum arranged in an alternating fashion. Each of these organelles is surrounded by an array of longitudionally orientated microtubules. The secretions are contained in membrane bound vesicles. In the type-4 cells the contents are homogeneous, whilst the other two contain distinctive electron-dense granules. The type-4 secretions are PAS negative and alcianophilic, the type-5 secretions are PAS positive and non-alcianophilic whilst the type-6 secretions have a strong affinity for Orange G.This work was supported by a grant from the Science Research Council.     

Sex steroids and stem cell function

Gender dimorphisms exist in the pathogenesis of a variety of cardiovascular, cardiopulmonary, neurodegenerative, and endocrine disorders. Estrogens exert immense influence on myocardial remodeling following ischemic insult, partially through paracrine growth hormone production by bone marrow mesenchymal stem cells (MSCs) and endothelial progenitor cells. Estrogens also facilitate the mobilization of endothelial progenitor cells to the ischemic myocardium and enhance neovascularization at the ischemic border zone. Moreover, estrogens limit pathological myocardial remodeling through the inhibitory effects on the proliferation of the cardiac fibroblasts. Androgens also may stimulate endothelial progenitor cell migration from the bone marrow, yet the larger role of androgens in disease pathogenesis is not well characterized. The beneficial effects of sex steroids include alteration of lipid metabolism in preadipocytes, modulation of bone metabolism and skeletal maturation, and prevention of osteoporosis through their effects on osteogenic precursors. In an example of sex steroid-specific effects, neural stem cells exhibit enhanced proliferation in response to estrogens, whereas androgens mediate inhibitory effects on their proliferation. Although stem cells can offer significant therapeutic benefits in various cardiovascular, neurodegenerative, endocrine disorders, and disorders of bone metabolism, a greater understanding of sex hormones on diverse stem cell populations is required to improve their ultimate clinical efficacy. In this review, we focus on the effects of estrogen and testosterone on various stem and progenitor cell types, and their relevant intracellular mechanisms.     

Olfactory responsiveness to two odorous steroids in three species of nonhuman primates

Social communication by means of odor signals is widespread among mammals. In pigs, for example, the C19-steroids 5-alpha-androst-16-en-3-one and 5-alpha-androst-16-en-3-ol are secreted by the boar and induce the mating stance in the sow. In humans, the same substances have been shown to be compounds of body odor and are presumed to affect human behavior. Using an instrumental conditioning paradigm, we here show that squirrel monkeys, spider monkeys and pigtail macaques are able to detect androstenone at concentrations in the micromolar range and thus at concentrations at least as low as those reported in pigs and humans. All three species of nonhuman primates were considerably less sensitive to androstenol, which was detected at concentrations in the millimolar range. Additional tests, using a habituation-dishabituation paradigm, showed that none of the 10 animals tested per species was anosmic to the two odorous steroids. These results suggest that androstenone and androstenol may be involved in olfactory communication in the primate species tested and that the specific anosmia to these odorants found in approximately 30% of human subjects may be due to their reduced number of functional olfactory receptor genes compared with nonhuman primates.     

Relationships between head morphology, bite performance and ecology in two species of Podarcis wall lizards

Understanding the relationship between form and function is central to our comprehension of how phenotypic diversity evolves. Traits involved in multiple activities, such as social interactions and ecological resource use, are under the influence of different evolutionary forces potentially acting in opposite directions. Such systems provide the opportunity of understanding how potential constraints on morphological variation may influence whole-organism performance. In this study we examined morphology and bite performance in two closely related species of Podarcis wall lizards with divergent microhabitat preferences, to investigate how natural and sexual selection interact to shape the evolution of head traits. Our results show that although head morphology is markedly different between species and sexes, only sexes differ in bite force, indicating that the ecological differentiation between species is reflected in their morphology but does not constrain performance. Rather, the modification of the relative size of head components between species and a shift in the form-function relationship provide a potential explanation of how equal performance is attained by different morphological configurations. Geometric morphometrics provide a clear, biomechanically meaningful image of how this is achieved and show a bisexual pattern of head shape-bite force association in both species. This, together with a strong allometry of head size on body size and head shape on head size, provides indirect morphological evidence for the importance of sexual selection in shaping morphological and functional patterns. Finally, our findings suggest that the differences observed between species and sexes in head traits and bite performance are not reflected in their dietary ecology, implying that if trophic niche segregation between groups occurs, the reasons behind it are not primarily related to head morphology and functional variation.     

Population dynamics of two species of dragon lizards in arid Australia: the effects of rainfall

The population dynamics of two species of agamid (dragon) lizards were studied in the Simpson Desert, central Australia, over a period of 7 years, and modelled in relation to rainfall. Both species have annual life cycles, with adults predominating during the breeding season in spring and summer and juveniles predominating in other seasons. Within years, juvenile abundance in both species in autumn and winter was related most strongly to rainfall in the preceding summer and autumn. This pattern suggests that rainfall enhances survival, growth and possibly clutch size and hatching success. Between years, however, rainfall drove successional change in the dominant plant species in the study area, spinifex Triodia basedowii, causing in turn a shift in the relative abundance of the two species. Thus, the central netted dragon Ctenophorus nuchalis was most numerous in 1990 when vegetation cover was <10%, but declined dramatically in abundance after heavy rainfall at the end of that year. In contrast, the military dragon C. isolepis achieved greatest abundance following heavy rains in the summers of 1990 and 1994, when spinifex cover increased to >20%, and remained numerically dominant for much of the study. We suggest that drought-wet cycles periodically reverse the dominance of the two species of Ctenophorus, and perhaps of other lizard species also, thus enhancing local species diversity over time. Further long-term studies are needed to document the population dynamics of other species, and to identify the factors that influence them. Received: 11 September 1998 / Accepted: 10 February 1999     

Associations between first encounters and ensuing social relations within dyads of two species of lacertid lizards

Researchers often presume that dominant individuals, duringan initial series of social interactions, ultimately gain possessionof the territory, but detailed studies of the process of socialrelation establishment in animals are rare. We used an experimentalapproach on pairs of conspecific newborns of two lizard species(Podarcis sicula and P. melisellensis) to examine whether theoutcomes of first encounters are consistent with the formationof social relations during the ensuing three weeks. A majorobjective was to determine whether social relations expressedduring prolonged cohabitation induced divergence of individualgrowth rates within a dyad. Moreover, we explored to what extentindividual differences in growth rate and behavior during socialcohabitation paralleled differences expressed when the animalswere housed in isolation. Differential expression of behaviorwithin dyads was examined by calculating the difference betweenvalues for the two individual lizards. During brief first encounters,access to a localized basking site was determined by agonisticinteractions between lizards. Cohabitation of two lizards duringprolonged encounters resulted in differences in their thermalmicrohabitat usage, which in turn induced divergence of theirgrowth rates. The direction and magnitude of the differencesin thermal microhabitat use and the divergence in growth ratesduring prolonged encounters mirrored differences in the interactionsexhibited during the first encounter. Moreover, differencesbetween two lizards in initial social interactions, and in thermalmicrohabitat use and growth rate during prolonged encounters,paralleled differences in thermal microhabitat use exhibitedwhen lizards were housed alone. Thus, it may be possible topredict the outcome of social interactions within dyads basedon the differential expression of traits between two lizardshoused in isolation.     

Sex chromosomes pairing in two Arvicolidae species: Microtus nivalis and Arvicola sapidus

Arvicolid rodents present both synaptic and asynaptic sex chromosomes. We analyzed the pairing behaviour of sex chromosomes in two species belonging to this rodent group (Microtus nivalis and Arvicola sapidus). At pachynema, the sex chromosomes of both species paired in a small region while the rest remain unsynapsed. Consequently at metaphase I, sex chromosomes present end-to-end association. Thus, the pairing behaviour of sex chromosomes in these species is very similar to that previously described for other arvicolid rodents and for most mammals. According to this, we propose that synaptic sex chromosomes were the ancestral condition in the family Arvicolidae, including the genus Microtus. The phylogenetic origin of the asynaptic sex chromosomes in the genus Microtus would have arisen once in the lineage that originated the species M. arvalis/agrestis and related species, while the lineage that originated the species M. oeconomous and related species conserved synaptic chromosomes. Furthermore, the phylogenetic relationships between the genus Microtus, Chionomys and Pitymys are discussed in relation to the synaptic behaviour of sex chromosomes.