Identification of a 130-kDa albumin in tuatara (Sphenodon) and detection of a novel albumin polymorphism

Electrophoretic, immunochemical, and protein sequence analyses were performed on plasma albumin of the tuatara (Sphenodon), a rare reptile endemic to New Zealand. The analyses revealed that, unlike other terrestrial vertebrates, tuatara do not seem to possess a 60- to 75-kDa plasma albumin. The common form of plasma albumin in this genus has an apparent molecular mass of 130 kDa, making it by far the largest albumin reported for any terrestrial vertebrate. Starch gel electrophoresis of samples from tuatara on 24 of the 30 islands inhabited by this genus resolved two forms of the 130-kDa albumin (albumins A and C). A third albumin of approximately 170 kDa (albumin B), reflecting a novel alloalbuminemia, was found in tuatara in three geographically isolated populations. Albumin A appears to be restricted to populations at the southern extremity of the tuatara's distribution, while albumin C was found in all but four (southern) populations. Possible explanations for the origin and distribution of these albumins are discussed.     

Ecology and dynamics of the blood parasite, Hepatozoon tuatarae (Apicomplexa), in tuatara (Sphenodon punctatus) on Stephens Island, New Zealand

We explored infection patterns and temporal dynamics of the protozoan blood parasite Hepatozoon tuatarae (Apicomplexa) infecting the tuatara (Sphenodon punctatus), a protected reptile living on Stephens Island, New Zealand. In March 2006, we surveyed tuatara in five study sites to examine spatial variation in infection prevalence, and four times, from May 2005 to November 2006, we recaptured marked individuals within three study sites to examine the temporal dynamics of infection. We also examined how blood-parasite infection patterns were influenced by host sex, body size, and host infestation with ticks (Amblyomma sphenodonti) and mites (Neotrombicula spp.), which are potential vectors of the blood parasite. Infection prevalence (16.9-24% infected) and intensity (<0.01-0.1% blood cells infected) were low in all samples. Infection intensity varied among the five sampled sites in March 2006, but prevalence did not. Neither infection prevalence nor intensity varied with time, and infections were detected in consecutive samples from recaptured individuals for up to 18 mo. Neither survey showed an influence of host sex on infection, but both surveys showed infection intensity declined with increasing host body size, as did infection prevalence in the spatial survey. In the temporal survey, we found a positive relationship between the tick numbers on hosts and blood-parasite infection intensity, which were stronger in two of the sampling periods and among larger hosts. These data suggest that exposure and susceptibility to infection decreases with host size and that ticks, but not mites, are probably the vectors in this ancient host-parasite association of a long-lived (>50 yr) host.     

Seasonal and spatial dynamics of ectoparasite infestation of a threatened reptile, the tuatara (Sphenodon punctatus)

Abstract The conservation of threatened vertebrate species and their threatened parasites requires an understanding of the factors influencing their distribution and dynamics. This is particularly important for species maintained in conservation reserves at high densities, where increased contact among hosts could lead to increased rates of parasitism. The tuatara (Sphenodon punctatus) (Reptilia: Sphenodontia) is a threatened reptile that persists at high densities in forests (～ 2700 tuatara/ha) and lower densities in pastures and shrubland (< 200 tuatara/ha) on Stephens Island, New Zealand. We investigated the lifecycles and seasonal dynamics of infestation of two ectoparasites (the tuatara tick, Amblyomma sphenodonti, and trombiculid mites, Neotrombicula sp.) in a mark‐recapture study in three forest study plots from November 2004 to March 2007, and compared infestation levels among habitat types in March 2006. Tick loads were lowest over summer and peaked from late autumn (May) until early spring (September). Mating and engorgement of female ticks was highest over spring, and larval tick loads subsequently increased in early autumn (March). Nymphal tick loads increased in September, and adult tick loads increased in May. Our findings suggest the tuatara tick has a 2‐ or 3‐year lifecycle. Mite loads were highest over summer and autumn, and peaked in March. Prevalences (proportion of hosts infected) and densities (estimated number of parasites per hectare) of ticks were similar among habitats, but tick loads (parasites per host) were higher in pastures than in forests and shrub. The prevalence and density of mites was higher in forests than in pasture or shrub, but mite loads were similar among habitats. We suggest that a higher density of tuatara in forests may reduce the ectoparasite loads of individuals through a dilution effect. Understanding host–parasite dynamics will help in the conservation management of both the host and its parasites.     

Introduction of the European minnow into a subalpine lake: habitat use and long-term changes in population dynamics

Minnows Phoxinus phoxinus , studied 30 years after the first record of the species in the subalpine Lake Øvre Heimdalsvatn, Norway, ≥55 mm L _T, were estimated to have densities of c . 4.7 kg ha⁻¹ (120 000 fish) in June 1999 and 2.1 kg ha⁻¹ (63 000 fish) in June 2000. The population was characterized by low individual growth, delayed age of maturity and lived longer when compared to values reported in a previous study in the early phase of its establishment, and other values reported in the literature. Most minnows reached sexual maturity at 4–5 years and >55 mm L _T. Although the estimated annual survival of minnows >55 mm was low ( S =0.2), ages up to 13 years were recorded. Despite a moderate increase in the population size during the last 20 years, the present reduction in individual growth, followed by delayed age of maturity, suggested the existence of density-dependent effects on the population dynamics of the minnows. The minnows were restricted to the littoral zone and near bottom areas. A vertical or horizontal expansion in habitat use was probably prevented by the presence of piscivorous brown trout Salmo trutta .     

Rapid temporal change in frequency of infanticide in a passerine bird associated with change in population density and body condition

Sexually selected infanticide, whereby unmated males obtaina mate by killing the dependent offspring of an already matedfemale, is a common alternative reproductive strategy in manyanimals. I estimated the frequency of infanticide in a populationof barn swallows, Hirundo rustica, during the period 1977–2002.Population size decreased by more than a factor 10 during thisperiod, and this decrease was associated with an increase inmortality, selecting for adults with better body condition.Density-dependent effects acted on infanticide through the relationshipbetween the relative number of unmated males and populationsize. Because males in prime condition are better able to defendtheir nests against infanticidal males, the frequency of infanticidedecreased as mean tail length and mean body condition of malesincreased during the study period. Therefore, a rapid decreasein population size, a decrease in the abundance of unmated males,and a concomitant increase in body condition have changed theimportance of infanticide from being a major cause of mortalityaccounting for more than 25% of all nestling mortality to beingalmost completely absent during a period of 25 years.     

Density dependence and population dynamics of black rhinos (Diceros bicornis michaeli) in Kenya’s rhino sanctuaries

Density‐dependent feedback mechanisms provide insights into the population dynamics and interactions of large herbivores with their ecosystem. Sex ratio also has particularly important implications for growth rates of many large mammal populations through its influence on reproductive potential. Therefore, the interrelationships between density‐dependent factors, comprising density, sex ratio and underlying growth rates (r) were examined for the Eastern black rhino (Diceros bicornis michaeli) living in three rhino sanctuaries in Kenya using four population models. The exponential and logistic models gave similar results and the former were accepted because they better portrayed the actual situation on the ground. Sex ratios in all sanctuary populations were positively correlated with r but interpreted with realization of other factors also affecting r. We caution that the results of population models should be interpreted alongside ground‐truthed observations. We recommend that future translocation strategies should take into account sex and age structures of the donor population, while future studies of density dependence should take into account both biotic and abiotic factors.     

Formation of the corneous layer in the epidermis of the tuatara (Sphenodon punctatus, Sphenodontida, Lepidosauria, Reptilia)

The formation of the stratum corneum in the epidermis of the reptile Sphenodon punctatus has been studied by histochemical, immunohistochemical, and ultrastructural methods. Sulfhydryl groups are present in the mesos and pre-alpha-layer but disappear in the keratinized beta-layer and in most of the mature alpha-layer. This suggests a complete cross-linking of keratin filaments. Tyrosine increases in keratinized layers, especially in the beta-layer. Arginine is present in living epidermal layers, in the presumptive alpha-layer, but decreases in keratinized layers. Histidine is present in corneous layers, especially in the intermediate region between the alpha- and a new beta-layer, but disappears in living layers. It is unknown whether histidine-rich proteins are produced in the intermediate region. Small keratohyalin-like granules are incorporated in the intermediate region. The plane of shedding, as confirmed from the study on molts, is located along the basalmost part of the alpha-layer and may involve the degradation of whole cells or cell junctions of the intermediate region. A specific shedding complex, like that of lizards and snakes, is not formed in tuatara epidermis. AE1-, AE2-, or AE3-positive alpha-keratins are present in different epidermal layers with a pattern similar to that previously described in reptiles. The AE1 antibody stains the basal and, less intensely, the first suprabasal layers. Pre-keratinized, alpha- and beta-layers, and the intermediate region remain unlabeled. The AE2 antibody stains suprabasal and forming alpha- and beta-layers, but does not stain the basal and suprabasal layers. In the mature beta-layer the immunostaining disappears. The AE3 antibody stains all epidermal layers but disappears in alpha- and beta-layers. Immunolocalization for chick scale beta-keratins labels the forming and mature beta-layer, but disappears in the mesos and alpha-layer. This suggests the presence of common epitopes in avian and reptilian beta-keratins. Low molecular weight alpha-keratins present in the basal layer are probably replaced by keratins of higher molecular weight in keratinizing layers (AE2-positive). This keratin pattern was probably established since the beginning of land adaptation in amniotes.     

Male-biased sex allocation in late-blooming flowers driven by resource limitation in the clonal perennial Aconitum kusnezoffii (Ranunculaceae)

Flowering phenology and clonal growth are known to affect resource and pollen availability, and therefore select for adaptive or constrained sex allocation strategies to some degree. However, the consequences of temporal sex allocation patterns for reproductive fitness across the flower, inflorescence, and genet levels have rarely been examined. Moreover, experimental tests of the underlying regulatory mechanisms are scarce. We examined the association of flowering phenology and inflorescence position with temporal sex allocation and reproductive success in the protandrous perennial clonal herb, Aconitum kusnezoffii, over four consecutive growing seasons by examining more than 39 000 flowers. We also conducted controlled experiments to test the effects of resource and pollen limitation on the female reproductive success of lateral inflorescences. We found that some male functions were positively correlated with flowering phenology, whereas female reproductive success was negatively correlated with flowering phenology and inflorescence position. Lateral inflorescences invested more in male function than terminal inflorescences and therefore yielded fewer and smaller seeds. Resource limitation may serve as the key mechanism underlying this differentiated pattern. Decreased female reproductive success was consistently observed at the flower and inflorescence levels as flowering occurred later in the growth season. Late-blooming lateral inflorescences specialized in the male function, and their female reproductive success was constrained by early-blooming terminal inflorescences. This might be the first attempt to systematically demonstrate sex allocation strategy differentiation in a protandrous plant species at the inflorescence level. In addition, our study provides empirical evidence of dichogamy selecting for specialized sex allocation strategies among inflorescences.     

Differences in dietary and plasma fatty acids between wild and captive populations of a rare reptile, the tuatara (Sphenodon punctatus)

Tuatara (Sphenodon) are rare reptiles endemic to New Zealand. Wild tuatara on Stephens Island (study population) prey on insects as well as the eggs and chicks of a small nesting seabird, the fairy prion (Pachyptila turtur). Tuatara in captivity (zoos) are fed diets containing different insects and lacking seabirds. We compared the fatty acid composition of major dietary items and plasma of wild and captive tuatara. Fairy prions (eaten by tuatara in the wild) were rich in C20 and C22 polyunsaturated fatty acids (PUFA), especially the n-3 fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). In contrast, items from the diet of captive tuatara contained no C20 and C22 PUFA and were higher in medium-chain and less unsaturated fatty acids. Plasma from wild tuatara was higher in n-3 PUFA [including alpha-linoleic acid (C18:3n-3), EPA and DHA], and generally lower in oleic acid (C18:1) and palmitic acid (C16:0), than plasma from captive tuatara in the various fractions (phospholipid, triacylglycerol, cholesterol ester and free fatty acids). Plasma from wild adult tuatara showed strong seasonal variation in fatty acid composition, reflecting seasonal consumption of fairy prions. Differences in the composition of diets and plasma between wild and captive tuatara may have consequences for growth and reproduction in captivity. Accepted: 3 August 1998     

Parasitism of a pollinator fig wasp: mortalities are higher in figs with more pollinators,but are not related to local densities of figs

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Pollen limitation and Allee effect related to population size and sex ratio in the endangered Ottelia acuminata (Hydrocharitaceae): implications for conservation and reintroduction

Small populations may suffer more severe pollen limitation and result in Allee effects. Sex ratio may also affect pollination and reproduction success in dioecious species, which is always overlooked when performing conservation and reintroduction tasks. In this study, we investigated whether and how population size and sex ratio affected pollen limitation and reproduction in the endangered Ottelia acuminata, a dioecious submerged species. We established experimental plots with increasing population size and male sex ratio. We observed insect visitation, estimated pollen limitation by hand‐pollinations and counted fruit set and seed production per fruit. Fruit set and seed production decreased significantly in small populations due to pollinator scarcity and thus suffered more severe pollen limitation. Although frequently visited, female‐biased larger populations also suffered severe pollen limitation due to few effective visits and insufficient pollen availability. Rising male ratio enhanced pollination service and hence reproduction. Unexpectedly, pollinator preferences did not cause reduced reproduction in male‐biased populations because of high pollen availability. However, reproductive outputs showed more variability in severe male‐biased populations. Our results revealed two component Allee effects in fruit set and seed production, mediated by pollen limitation in O. acuminata. Moreover, reproduction decreased significantly in larger female‐biased populations, increasing the risk of an Allee effect.     

Experimental assessment of the fecundity of Eucypris virens (Ostracoda, Crustacea) under natural sex ratios

1. The adaptive significance of the observed variations in sex ratios in non‐marine ostracods is unclear. This study quantified the fecundity of females taken from a presumed fully sexual Eucypris virens population that were experimentally combined with different proportions of males (male : female sex ratios: 1 : 1, 1 : 2, 1 : 4, 1 : 8 and 0 : 1). 2. The results yielded no indications that female fecundity is altered by short‐term variations in the proportion of males, at least not within the range of sex ratios that are common in natural ostracod populations. Complete removal of males, however, did strongly reduce hatching success of dried eggs. This suggests the need for multiple mating events during the reproductive lifetime of the female. It also emphasizes the need for a minimum number of males, although this minimum number evidently may be rather low, as we found a high number of spermatozoa in the seminal receptacles after a single mating event. 3. The sex ratio in the source population was strongly female biased (1 : 3.4; n = 514), whereas in the hatchling assemblages reared in the laboratory, males and females were found in equal proportions (1 : 1.0; n = 1516), irrespective of the prevailing sex ratio. This clear discrepancy is intriguing, and points to the importance of epigenetic factors for the determination of field sex ratios.     

Variation in Population and Life History Traits of the American Eel, Anguilla rostrata, in Four Rivers in Maine

We examined population traits of yellow American eels from nine sites with similar habitat characteristics in each of four rivers in Maine, U.S.A. Migrating silver eels were also collected to compare sex ratio, age and size at migration among the four rivers. Population density and biomass were not significantly different among rivers with mean ranges of 8.4–21.8 eels 100m^–2and 380–1485gm^–2. Pairwise comparisons of the slopes of weight–length relationships of log transformed data (pooled data: intercept = –6.007, slope = 3.094, r²= 0.99, and n = 3116) revealed no significant differences among rivers. Length–age relationships (pooled data: intercept = 87.826, slope = 23.444, r²= 0.76, and n = 2325) also showed no statistically significant pairwise differences in slopes among rivers. In all rivers, sexual differentiation was complete by 270mm total length and age eleven. The sex ratios of migrating silver eels were not correlated with yellow eel sex ratios among the four rivers. Mean age at migration among the four rivers was significantly different for males only, with a range of 1.3years. Both sexes had some significant differences in size at migration among rivers, but the biological importance of the differences is tenuous (male range: 15mm, female range: 36mm). The yellow and silver eel population traits from these four rivers showed little variation when riverine habitat was isolated. Variations in traits appeared to be greater when eels from non-riverine habitats may have been present.     

Maternal condition and offspring sex ratio in polygynous ungulates: a case study of bighorn sheep

The Trivers and Willard model (TWM) predicts that for sexuallydimorphic polygynous mammals, mothers able to provide a highlevel of care should bias offspring sex ratio in favor of sons.Contradictory results of empirical studies, however, suggestthat selective pressures for adaptive offspring sex ratio varywith species and environmental conditions. We report the resultsof a 29-year study of marked bighorn sheep (Ovis canadensis)in a population that underwent wide changes in density and wheremost females were weighed each year. Lamb sex ratio was independentof absolute ewe mass and yearly deviations from individual orpopulation average mass, but there was a nonsignificant trendtowards fewer males being born at high population density. Bighornsheep satisfy all the assumptions of the TWM but not its prediction:lamb sex ratio is independent of maternal ability to providecare. Recent hypotheses to explain the lack of relationshipbetween maternal condition and offspring sex in ungulates areunlikely to apply to bighorn sheep. We suggest that the TWMmay only apply when social rank strongly affects the abilityto provide maternal care. Those circumstances are likely tooccur for only a few species and within a narrow range of environmentalconditions.     

Individual variation in body color in the field cricket Teleogryllus occipitalis (Orthoptera: Gryllidae)

Body color of animals may affect individual fitness through direct effects on various processes, such as predatory avoidance, thermoregulation, UV resistance, and mating behavior. Body color variation of the field cricket Teleogryllus occipitalis (Audinet‐Serville) (Orthoptera: Gryllidae) is often observed. We quantified the individual variation in body color of this species by measuring the luminance of hind leg femur. Thereafter, we examined whether the body color was a heritable trait or not using parent–offspring analysis. In addition, the effect of body color of both parents on body size, sex ratio, and survival rate of progeny was investigated. The results showed that maternal body color was not heritable, whereas paternal body color was correlated with the body color of the progeny. Body size and sex ratio were not correlated with body color of parents. Although paternal body color did not affect the survival rate of the progeny beyond the stage of final instar nymph, progeny survival rate significantly increased with darkness of maternal body.     

Predation Risk Drives Habitat‐Specific Sex Ratio in a Monomorphic Species,the Brown Hare (Lepus europaeus)

In dimorphic species, sexual habitat segregation is generally explained by the differences in nutritional needs or by a trade‐off between fulfilling food requirements and avoiding predation. However, it remains unclear whether predation risk is strong enough to drive the differences in habitat use between sexes as predicted by the predation sensitivity hypothesis. Here we test in a monomorphic species, the brown hare (Lepus europaeus), the prediction that abundance of the gender more sensitive to predation is higher in safer habitat. We used data on 1645 individually marked hares in western Poland during autumn–winter seasons of 1966/1967–1978/1979 to estimate sex‐specific annual survival rates. We analyzed the stomach contents of 134 foxes shot in 1965/1966–1994/1995 to evaluate fox predation on hares. Finally, we employed data on 26 790 hares live‐trapped in 1965/1966–1994/1995 to analyze hare sex ratio across habitats. We found that male annual survival rate was lower than that of females and that the predation risk by foxes on hares was lower in agricultural than forest habitat. Our finding, that males were more often trapped by nets in agricultural than the forest habitat, provides indirect evidence for the predation sensitivity hypothesis. We conclude that predation risk can be a driving force for habitat‐specific sex ratio in a monomorphic species such as the brown hare.     

Resource competition between genetically varied and genetically uniform populations of Daphnia pulex (Leydig): does sexual reproduction confer a short‐term ecological advantage?

Small competitive advantages may suffice to compensate for a large disadvantage in intrinsic growth capacity. This well‐known principle from ecology has recently been applied to the enduring question of how sexual reproduction can persist in the face of invasion by female‐only parthenogens. Small competitive advantages resulting directly from sexual reproduction are predicted to cancel a two‐fold disadvantage in intrinsic growth capacity caused by males (which do not themselves produce offspring) comprising half the sexual population. In this paper we test the principal assumption of this theory, that the genetic variation produced by sexual reproduction confers a competitive advantage over self‐identical asexual invaders. We set up competition between a diverse clonal assembly of Daphnia pulex and genetically uniform populations from single clones. At young ages, the population comprising genetically varied Daphnia had significantly higher birth rates in competition with populations of genetically uniform Daphnia than in competition with itself, indicating competitive release and a Lotka–Volterra competition coefficient α₁₂ < 1. No such difference was apparent under conditions of greater food stress, possibly due to individuals channelling more energy into survival, or for old‐aged populations, possibly as a result of reduced selective pressures for high reproduction in old females. Mean birth rates differed between the clones at all ages in the presence of competition, providing evidence of variation in life history traits between clones. A Lotka–Volterra model predicted empirical estimates of α₁₂ = 0.896 (genetically uniform on varied) and α₂₁ = 1.010 (varied on uniform), which permits immediate coexistence of a sexual population of D. pulex even with an asexual lineage having twice the intrinsic growth capacity. © 2005 The Linnean Society of London, Biological Journal of the Linnean Society, 2005, 85 , 111–123.