Animal Life History Research Articles

Life history events of the Eurasian sparrowhawk Accipiter nisus in a changing climate

Current climate change has been found to advance spring arrival and breeding dates of birds, but the effects on autumn migration and possible responses in the distribution of wintering individuals are poorly known. To thoroughly understand the consequences of climate change for animal life histories and populations, exploration of whole annual cycles are needed. We studied timing of migration (years 1979–2007), breeding phenology (1979–2007) and breeding success (1973–2007) of Eurasian sparrowhawks Accipiter nisus in Finland. We also investigated whether the migration distance of Finnish sparrowhawks has changed since the 1960s, using ringing recovery records. Since the late 1970s Finnish sparrowhawks have advanced their spring arrival, breeding and autumn departure considerably, but the migration distance has not changed. Early migrants, who are the ones with the highest reproductive success, show the strongest advance in the timing of spring migration. In autumn, advanced departure concerns young sparrowhawks. Late autumn migrants, who are mainly adults, have not advanced their migration significantly. The sparrowhawk is the most common bird of prey and the main predator of most passerines in Finland. Therefore, changes in sparrowhawk migration phenology may affect the migration behaviour of many prey species. The breeding success of sparrowhawks has increased significantly over the study period. This is however more likely caused by other factors than climate change, such as reduced exposure to organochlorine pollutants.

Fast and furious: effects of body size on strike performance in an arboreal viperTrimeresurus(Cryptelytrops)albolabris

Body size has a pervasive effect on animal functioning and life history with size dependent changes in performance and physiology throughout ontogeny being common in many ectothermic vertebrates. However, as selection on juvenile life history stages is strong, juveniles often offset the disadvantages of small body size by disproportionate levels of performance. Here, we investigate size-related changes in defensive strike performance in an arboreal pit viper, Trimerusurus (Cryptelytrops) albolabris. Our data show a significant negative allometry in the scaling of head dimensions and head mass to body mass. However, strike velocity and strike distance are independent of body mass, with juveniles in our sample striking as fast and as far as adults. In contrast to model predictions suggesting that acceleration capacity should decrease with increasing body mass, acceleration capacity increases with snake body mass. Our results suggest that this is the result of a negative allometric scaling of head mass combined with an isometric scaling of the dorsal epaxial musculature. Finally, our data show a significant sexual dimorphism in body size and strike velocity with females being heavier and striking faster independent of the dimorphism in body size.

Carry-over effects as drivers of fitness differences in animals

1. Carry-over effects occur when processes in one season influence the success of an individual in the following season. This phenomenon has the potential to explain a large amount of variation in individual fitness, but so far has only been described in a limited number of species. This is largely due to difficulties associated with tracking individuals between periods of the annual cycle, but also because of a lack of research specifically designed to examine hypotheses related to carry-over effects. 2. We review the known mechanisms that drive carry-over effects, most notably macronutrient supply, and highlight the types of life histories and ecological situations where we would expect them to most often occur. We also identify a number of other potential mechanisms that require investigation, including micronutrients such as antioxidants. 3. We propose a series of experiments designed to estimate the relative contributions of extrinsic and intrinsic quality effects in the pre-breeding season, which in turn will allow an accurate estimation of the magnitude of carry-over effects. To date this has proven immensely difficult, and we hope that the experimental frameworks described here will stimulate new avenues of research vital to advancing our understanding of how carry-over effects can shape animal life histories. 4. We also explore the potential of state-dependent modelling as a tool for investigating carry-over effects, most notably for its ability to calculate optimal rates of acquisition of a multitude of resources over the course of the annual cycle, and also because it allows us to vary the strength of density-dependent relationships which can alter the magnitude of carry-over effects in either a synergistic or agonistic fashion. 5. In conclusion carry-over effects are likely to be far more widespread than currently indicated, and they are likely to be driven by a multitude of factors including both macro- and micronutrients. For this reason they could feasibly be responsible for a large amount of the observed variation in performance among individuals, and consequently warrant a wealth of new research designed specifically to decompose components of variation in fitness attributes related to processes across and within seasons.

Frontiers in Respiratory Physiology - Grand Challenge

Frontiers in Respiratory Physiology - Grand Challenge

Effects of temperature and food availability on growth and reproduction in the neustonic pedunculate barnacle Lepas anserifera

To elucidate the life history of neustonic animals, growth and reproductive patterns were investigated in the hermaphroditic pedunculate barnacle Lepas anserifera in field and laboratory experiments in Wakayama, western Japan from 2006 to 2008. The effects of temperature (19, 24 or 29°C) and food availability (once or twice a week) on growth and reproduction were also studied in the laboratory. The barnacles grew and matured rapidly, especially in the field: individuals on the average grew from 3 mm to more than 12 mm in capitulum length within 15 days and some were brooding. High temperature and high food availability resulted in greater growth. High temperature also resulted in earlier maturation of both testes and ovaries, whereas the effect of food availability was less clear. The rapid growth and maturation, together with earlier maturation at higher temperatures, may be an adaptation to ephemeral floating objects to which they attach.

Brain size of the lion (Panthera leo) and the tiger (P. tigris): implications for intrageneric phylogeny, intraspecific differences and the effects of captivity

Intraspecific encephalization of the lion and the tiger is investigated for the first time using a very large sample. Using cranial volume as a measure of brain size, the tiger has a larger brain relative to greatest length of skull than the lion, the leopard and the jaguar. The Asian lion has a relatively much smaller brain compared with those of sub-Saharan lions, between which there are few differences. The Balinese and Javan tigers had relatively larger brains compared with those of Malayan and Sumatran tigers, even although these four putative subspecies occupy adjacent ranges in south-eastern Asia. Differences in brain size do not appear to correlate with any known differences in behaviour and ecology and, therefore, may reflect only chance differences in intrageneric and intraspecific phylogeny. However, captive-bred big cats generally have a reduced brain size compared with that of wild animals, so that an animal's life history and living conditions may affect brain size and, hence, functional or environmental explanations should be considered when linking brain size differences to intraspecific phylogenies.

Biologia reprodutiva de Elaenia cristata (Aves: Tyrannidae) em cerrado do Brasil central

Reproduction is a fundamental biological process to animal life histories and includes risks which affect the survival of breeding adults. Considering that information about Elaenia cristata reproduction biology is lacking, we aimed in this study to describe some aspects related to its reproduction. We carried out this study from 2002 to 2007 at “Estacao Ecologica de Aguas Emendadas” (ESEC-AE) and its surroundings, within the Cerrado biome, Distrito Federal, Brazil. We monitored 89 nests every 2-4 days. The breeding season started in September, had a peak in October and lasted until early December, with an average length of 99 days. Elaenia cristata builds its open cup nests on a fork. Clutch size was mostly of two eggs (n = 50). Its eggs are white with or without small brownish dots around the obtuse end. Egg length and width (n = 7) averaged 20.2 ± 0.1 mm and 15.1 ± 0.1 mm, respectively. Nest height above the ground (n = 87) averaged 1.5 ± 0.8 m, most of them on Davilla elliptica. Cerrado sensu strictu was the habitat most used (61%) for nest building. The incubation period averaged 15.2 ± 0.5 days (n = 9), while the nestling period averaged 16.4 ± 0.4 days (n = 17). Egg success was 31.4% and mean hatching rate was 0.95 ± 0.1. Overall productivity was 0.5 ± 0.5 fl edgling per nest, and fecundity rate was 0.9 ± 0.6 fl edgling per female. Nineteen nests were successful (27%) and 51 were depredated (73%). Predation rate during the incubation phase (71%) was higher than during the nestling phase (29%), contrary to the pattern found in most birds. However, the other reproductive aspects are similar to those described for its congeners, other flycatchers or most Neotropical passerines

Evaluation onto life cycle parameters of Ceriodaphnia silvestrii submitted to 36 days dietary copper exposure

The present study aimed to investigate the response of several life history parameters (body length and age of primipara, duration of embryonic development, maximum body length, reproduction and survival) of the zooplankton Ceriodaphnia silvestrii while exposed to copper contaminated algae Pseudokirchneriella subcapitata. In order to evaluate chronic exposure on the animal's life history, long-term experimental design was used. Cladocerans were fed with a dietary copper concentration ranging from 3 to 68 fg Cu cell −1. Low waterborne copper exposure (around 10 −10 mol L −1 free Cu 2+ ions) was kept in the experiments. The results showed that by exposure of cladocerans during 7 days to contaminated food with 68 fg Cu cell −1, a significant reduction in neonate production, survival and body size were obtained. Inhibition on egg production of zooplankton at 38 fg Cu cell −1 were observed in 36 days chronic dietary copper exposure. The importance of entire life cycle study to better evaluate cladoceran responses to chronic dietary metal exposure was demonstrated.

New Protocetid Whale from the Middle Eocene of Pakistan: Birth on Land, Precocial Development, and Sexual Dimorphism

BackgroundProtocetidae are middle Eocene (49–37 Ma) archaeocete predators ancestral to later whales. They are found in marine sedimentary rocks, but retain four legs and were not yet fully aquatic. Protocetids have been interpreted as amphibious, feeding in the sea but returning to land to rest.Methodology/Principal FindingsTwo adult skeletons of a new 2.6 meter long protocetid, Maiacetus inuus, are described from the early middle Eocene Habib Rahi Formation of Pakistan. M. inuus differs from contemporary archaic whales in having a fused mandibular symphysis, distinctive astragalus bones in the ankle, and a less hind-limb dominated postcranial skeleton. One adult skeleton is female and bears the skull and partial skeleton of a single large near-term fetus. The fetal skeleton is positioned for head-first delivery, which typifies land mammals but not extant whales, evidence that birth took place on land. The fetal skeleton has permanent first molars well mineralized, which indicates precocial development at birth. Precocial development, with attendant size and mobility, were as critical for survival of a neonate at the land-sea interface in the Eocene as they are today. The second adult skeleton is the most complete known for a protocetid. The vertebral column, preserved in articulation, has 7 cervicals, 13 thoracics, 6 lumbars, 4 sacrals, and 21 caudals. All four limbs are preserved with hands and feet. This adult is 12% larger in linear dimensions than the female skeleton, on average, has canine teeth that are 20% larger, and is interpreted as male. Moderate sexual dimorphism indicates limited male-male competition during breeding, which in turn suggests little aggregation of food or shelter in the environment inhabited by protocetids.Conclusions/SignificanceDiscovery of a near-term fetus positioned for head-first delivery provides important evidence that early protocetid whales gave birth on land. This is consistent with skeletal morphology enabling Maiacetus to support its weight on land and corroborates previous ideas that protocetids were amphibious. Specimens this complete are virtual ‘Rosetta stones’ providing insight into functional capabilities and life history of extinct animals that cannot be gained any other way.

Phanerozoic trends in the global geographic disparity of marine biotas

Previous analyses of the history of Phanerozoic marine biodiversity suggested that the post-Paleozoic increase observed at the family level and below was caused, in part, by an increase in global provinciality associated with the breakup of Pangea. Efforts to characterize the Phanerozoic history of provinciality, however, have been compromised by interval-to-interval variations in the methods and standards used by researchers to calibrate the number of provinces. With the development of comprehensive, occurrence-based data repositories such as the Paleobiology Database (PaleoDB), it is now possible to analyze directly the degree of global compositional disparity as a function of geographic distance (geo-disparity) and changes thereof throughout the history of marine animal life. Here, we present a protocol for assessing the Phanerozoic history of geo-disparity, and we apply it to stratigraphic bins arrayed throughout the Phanerozoic for which data were accessed from the PaleoDB. Our analyses provide no indication of a secular Phanerozoic increase in geo-disparity. Furthermore, fundamental characteristics of geo-disparity may have changed from era to era in concert with changes to marine venues, although these patterns will require further scrutiny in future investigations.

Predation‐induced plasticity in metamorphic duration inXenopus laevis

Summary 1. Many organisms are able to vary the duration of life-history stages in response to environmental conditions such as predation risk. However, in those undergoing a metamorphosis, it is not known whether the duration of the metamorphic phase itself can change in response to the presence of a predator, and whether this carries costs. 2. In experiments using the amphibian Xenopus laevis , we found that metamorphosis was accelerated in the presence of a predator and this occurred consistently across the natural range of temperatures experienced by Xenopus . 3. Although metamorphic climax was reduced in duration, a functional tail was maintained for longer in the presence of a predator. Furthermore, burst swimming speed was significantly faster for animals metamorphosing in the presence than in the absence of a predator. This suggests that the more rapid development induced by predator presence does not carry costs in terms of ability to escape predators during metamorphosis. 4. There was no evidence of post-metamorphic costs of faster metamorphic climax in terms of escape response since juveniles from the two predator treatments did not differ in burst swimming speed. However, individuals metamorphosing in the presence of predators lost proportionally more mass during metamorphosis, resulting in smaller juveniles than those without predators. This reduced juvenile size represents a potential cost of accelerating metamorphic development. 5. Therefore, conditions experienced during metamorphic climax, independent of larval conditions, can have a significant influence on the life histories of animals with complex life cycles.

Lipids and lifespans: Constants and contradictions

With these unique data on echidna lipids, 'Tony' A.J. Hulbert and colleagues have added an important phylogenetic link to the allometric relationships of the polyunsaturated fatty acids (PUFAs) of membrane lipids to basal metabolic rate (BMR) and lifespan. Extensive studies in the past decade have developed the allometry of the membrane peroxidation index (PI), as calculated from the proportion of double bonds in fatty acids of membranes from heart and skeletal muscle. To a first approximation, a 25% decrease in PI from lower PUFA content doubles the lifespan. According to chemical principles (limited data is cited), the relative numbers of double bonds in hydrocarbon chains predicts their oxidizability. The very long echidna lifespan was not predicted by the allometric relationship of lifespan on body size, but was predicted by the PI calculated for skeletal muscle or liver mitochondria. Hulbert’s group has found these relationships throughout vertebrates and even invertebrates: the ultra-long-lived naked mole-rat vs lab mice (Mitchell et al 2008); birds (long-lived procellariforms vs short-lived galliforms) (Buttemer et al 2008); and bee castes (queen vs worker) (Haddad et al. 2007). All these ‘con-pairs’ show inverse relationships of lifespan to the PI index. Hulbert et al. have also probed these these relationships experimentally. Calorie restriction in mice, which increases lifespan, also lowered the PUFA content of muscle and the calculated PI, as predicted (Faulks et al 2006). Diet also has a major influence on the PUFA content and PI of honeybee castes (Haddad et al. 2007). Moreover, in vitro manipulation of levels of PUFAs in lipid bilayers (“species cross-over” experiments) caused corresponding changes in Na+K+ ATPase and other key membrane activities (Hulbert, 2007). The biophysics involved is still speculative. The allometric matrix relating biochemical and metabolic parameters to lifespan and other whole animal (macroscopic) life history traits may get as close as biology can to having regularities like those in the Periodic Table of the Elements (Finch 1990, Chapter 5). A contradiction arises about interpreting the PI from the naked-mole rat, which shows high levels of oxidation contrary to prediction. The naked-mole rat lives almost 10-fold longer than lab mice of the same size, just as predicted by the low PI for its size (Mitchell et al. 2007). Despite the calculated 2-fold lower lipid PI in most tissues, others reported that the naked-mole rat has 10-fold higher urinary isoprostanes and 2-fold or more oxidative damage to tissue DNA, lipids, and proteins than mice of the same age (Andziak et al 2006). The contrast of brain to the PI allometry of other organs, the importance of diet to tissue lipids, and the disconnect between the calculated PI and the observed levels of oxidative damage in some species are caveats for temperance in the joys of allometry. Of course, the level of oxidation is controlled by many processes beyond the lipid composition which are not represented by the PI. Moreover, the brain, however, deviates from the regularity of organ allometry in lipids and lifespans. Brain lipid PI is high across the mammals, mainly due to high levels of the highly oxidizable PUFA, docosahexanoic acid (DHA, 22:6 n-3) (Hulbert, 2006). DHA is 16% of the total phospholipid acyl chains in brain and has allometric coefficients on body size (M) that are very low relative to other organs: in brain, DHA~ Mexp-0.01; in heart, Mexp-0.40 (Hulbert et al 2002). [this study did not include human brain data]. Humans are notable for lower synthesis of DHA than most mammals, and for the importance of dietary DHA to optimum somatic growth and cognitive development (Brenna, 2002; Finch and Stanford, 2004). In Alzheimer transgenic mice, DHA supplements lowed brain amyloid accumulation (Lim et al. 2005). An important future goal is to undersand species differences in lipid biosynthesis. Hulbert observes, correctly in my view, that peroxisomal enzymes which synthesize PUFAs (desaturases and elongases) merit comparative studies. Besides raw sequence comparative genomics of coding and regulatory sequences, I suggest looking at DNA methylation, which was just shown to mediate social caste differentiation (Kurcharski et al 2008) and thence the observed differences in lipid composition and predicted PI. There are also interesting questions about human evolution, the PUFA dietary intake and biosynthesis, and increased longevity (Finch and Stanford, 2004; Finch 2007): During the last 2–3 million years of human evolution, our ancestors changed gradually from plant-based diets to the global preference of H sapiens for meat-rich diets with high PUFA content (Finch and Stanford, 2004). And 30 years was added to the lifespan. Besides the evolved changes in apolipoprotein E isoforms which influence blood lipid composition, human fibroblasts have higher expression of the peroxisomal enzyme phytanoyl-CoA 2-hydroxylase (Karaman et al. 2003). Both genomic and lipidomic studies may give further insights about how humans evolved the longest primate lifespan.

The impact of experimentally elevated energy expenditure on oxidative stress and lifespan in the short-tailed field voleMicrotus agrestis

Life-history theory assumes that animal life histories are a consequence of trade-offs between current activities and future reproductive performance or survival, because resource supply is limited. Empirical evidence for such trade-offs in the wild are common, yet investigations of the underlying mechanisms are rare. Life-history trade-offs may have both physiological and ecological mediated costs. One hypothesized physiological mechanism is that elevated energy metabolism may increase reactive oxygen species production, leading to somatic damage and thus compromising future survival. We investigated the impact of experimentally elevated energy expenditure on oxidative damage, protection and lifespan in short-tailed field voles (Microtus agrestis) maintained in captivity to remove any confounding ecological factor effects. Energy expenditure was elevated via lifelong cold exposure (7+/-2 degrees C), relative to siblings in the warm (22+/-2 degrees C). No treatment effect on cumulative mortality risk was observed, with negligible effects on oxidative stress and antioxidant protection. These data suggest that in captive animals physiologically mediated costs on life history do not result from increased energy expenditure and consequent elevations in oxidative stress and reduced survival.

Does Habitat Structure Affect Body Condition of Nestlings? A Case Study with Woodland Great TitsParus major

A large number of studies have demonstrated that habitat characteristics have a huge impact on all aspects of animal life history. This hypothesis predicts a relationship between habitat structure and the main components of fitness and, consequently, also predicts a relationship between habitat structure and other traits indirectly related to fitness, such as condition or health. We tested whether there was any relationship between the characteristics of a pine forest in the Iberian Peninsula and the condition of Great Tit nestlings reared in that forest. The parameters used to estimate nestling condition were weight, haematocrit and the presence of haemoparasites. The results suggest that mature forests produced nestlings in better condition but with a higher prevalence of haemoparasites than young forest, possibly because mature forests are a good habitat for both the bird and the parasite vector.

Considering the Case for Biodiversity Cycles: Re-Examining the Evidence for Periodicity in the Fossil Record

We re-examine the evidence for a 62 million year (Myr) periodicity in biodiversity throughout the Phanerozoic history of animal life reported by [1], as well as related questions of periodicity in origination and extinction. We find that the signal is robust against variations in methods of analysis, and is based on fluctuations in the Paleozoic and a substantial part of the Mesozoic. Examination of origination and extinction is somewhat ambiguous, with results depending upon procedure. Origination and extinction intensity as defined by [1] may be affected by an artifact at 27 Myr in the duration of stratigraphic intervals. Nevertheless, when a procedure free of this artifact is implemented, the 27 Myr periodicity appears in origination, suggesting that the artifact may ultimately be based on a signal in the data. A 62 Myr feature appears in extinction, when this same procedure is used. We conclude that evidence for a periodicity at 62 Myr is robust, and evidence for periodicity at approximately 27 Myr is also present, albeit more ambiguous.

Prolonged Permian Triassic ecological crisis recorded by molluscan dominance in Late Permian offshore assemblages.

The end-Permian mass extinction was the largest biotic crisis in the history of animal life, eliminating as many as 95% of all species and dramatically altering the ecological structure of marine communities. Although the causes of this pronounced ecosystem shift have been widely debated, the broad consensus based on inferences from global taxonomic diversity patterns suggests that the shift from abundant brachiopods to dominant molluscs was abrupt and largely driven by the catastrophic effects of the end-Permian mass extinction. Here we analyze relative abundance counts of >33,000 fossil individuals from 24 silicified Middle and Late Permian paleocommunities, documenting a substantial ecological shift to numerical dominance by molluscs in the Late Permian, before the major taxonomic shift at the end-Permian mass extinction. This ecological change was coincident with the development of fluctuating anoxic conditions in deep marine basins, suggesting that numerical dominance by more tolerant molluscs may have been driven by variably stressful environmental conditions. Recognition of substantial ecological deterioration in the Late Permian also implies that the end-Permian extinction was the climax of a protracted environmental crisis. Although the Late Permian shift to molluscan dominance was a pronounced ecological change, quantitative counts of 847 Carboniferous-Cretaceous collections from the Paleobiology Database indicate that it was only the first stage in a stepwise transition that culminated with the final shift to molluscan dominance in the Late Jurassic. Therefore, the ecological transition from brachiopods to bivalves was more protracted and complex than their simple Permian-Triassic switch in diversity.

High frequency of multiple paternity in the largest rookery of Mediterranean loggerhead sea turtles

Mating systems are a central component in the evolution of animal life histories and in conservation genetics. The patterns of male reproductive skew and of paternal shares in batches of offspring, for example, affect genetic effective population size. A prominent characteristic of mating systems of sea turtles seem to be a considerable intra- and interspecific variability in the degree of polyandry. Because of the difficulty of observing the mating behaviour of sea turtles directly in the open sea, genetic paternity analysis is particularly useful for gaining insights into this aspect of their reproductive behaviour. We investigated patterns of multiple paternity in clutches of loggerhead sea turtles in the largest Mediterranean rookery using four highly variable microsatellite loci. Furthermore, we tested for a relationship between the number of fathers detected in clutches and body size of females. More than one father was detected in the clutches of 14 out of 15 females, with two clutches revealing the contribution of at least five males. In more than half the cases, the contributions of different fathers to a clutch did not depart from equality. The number of detected fathers significantly increased with increasing female body size. This relationship indicates that males may prefer to mate with large, and therefore productive, females. Our results suggest that polyandry is likely to increase effective population size compared to a population in which females would mate with only one male; male reproductive contributions being equal.

Is the umbo matrix of bivalve shells ( Laternula elliptica) a climate archive?

Heavy metal accumulation into bivalve soft tissues has received increasing interest in recent years with respect to biomonitoring of environmental change including pollution. To a lesser extent, accretion of elements from the environment into bivalve hard structures (shells) has been investigated, although the importance of the shells as environmental archives has been acknowledged. Here we report element distribution within consecutive growth bands in the shells of the Antarctic soft shell clam Laternula elliptica, which is currently exposed to vast environmental change in Antarctic Peninsula coastal environments that undergo rapid climate warming. We performed a high spatial resolution analysis for Al, Fe, Mn, Cu, Pb and U in the shell umbo, by means of laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Element ratios within the umbo did not resemble either the ratios in the surrounding seawater, the sedimenting material in Potter Cove, or even the Earth's crust basal composition. Mn and Cu were preferentially incorporated into the umbo. A strong decrease of element accretion with time could be related to lifetime respiration mass ( R) of the animals. This indicates element accretion into the umbo and shell matrix to be largely a function of animal ecophysiology and life history, and these effects need to be considered in the context of potential usefulness of L. elliptica shells as environmental archives.

The role of intrinsic factors for the recruitment process in long-lived birds

Recruitment to the breeding population is one of the most important and complex steps in the life history of long-lived animals, with great consequences for their reproductive career. Longitudinal data on individuals has provided new information on recruitment to the natal colony. We approach recruitment from the individual level, and address intrinsic factors affecting the probability of recruitment. Key steps to recruitment to the natal colony are fledging, subadult survival, the return to the natal area, the decision to breed there, and the ability to do so. Determinants characterising the state of an individual before recruitment can have a genetic basis (such as sex, mass) or can originate from the individual’s experience (e.g. degree of parental care, number of siblings and rearing conditions affecting mass and age at fledging—or length of the subadult period). Recruitment depends also on age, experience and body condition, increasing with the number of prospecting years spent at the colony. Threshold levels in body mass and arrival in due time are preconditions to successful first breeding. The improvement of body condition with age may be mainly due to an increase in foraging efficiency, increasing the resources which can be allocated to reproduction beyond those needed for self-maintenance. Prospecting and attendance leads to the acquisition of skills favouring recruitment, concerned with establishing a territory, mating, courtship and chick feeding. It is suggested that the individual optimal age of recruitment is produced by balancing the risk of premature breeding, with the consequent reduction in survival, against the advantage of presumed increased breeding opportunities with the concomitant increase in lifetime reproductive success.

CHEMICAL DISCRIMINATION OF FOOD, CONSPECIFICS AND PREDATORS BY APPARENTLY VISUALLY-ORIENTED DIURNAL GECKOS, NAULTINUS MANUKANUS

Animal life history strategies evolve in response to a range of selective pressures, and often are tightly linked to sensory cues. Squamate reptiles possess well-developed chemosensory systems, which evolved early in their history and remain highly conserved. However, chemosensory abilities are secondarily reduced in primarily visual agamid and chameleonid lizards, which casts doubt on the ubiquity of reliance on chemosensory cues among squamates. Diurnal geckos from New Zealand avoid predators using visual crypsis and are primarily ambush foragers; reliance on visual cues may be a product of strong avian predation pressure and minimal influence from mammals and snakes for the past 80 my. We used New Zealand's diurnal geckos to test the role of local adaptation versus evolutionary conservatism in defining chemosensory systems. Specifically, we tested whether Marlborough green geckos, Naultinus manukanus, use chemoreception to detect and behaviorally respond to (1) food, (2) opposite-sex conspecifics, and (3) native reptilian predators (tuatara, Sphenodon punctatus). Chemosensory cues mediated gecko interactions with all three stimuli tested: (1) the scent of fruit induced greater exploratory behavior, (2) male geckos responded to scent of female conspecifics by increasing lingual sampling and activity, and (3) tuatara fecal cues (but not skin secretions) elicited characteristic antipredator freeze behavior in geckos. Neither the primarily visual life history strategies nor the reduced range of predators of New Zealand's diurnal geckos appears to have reduced their chemosensory abilities relative to other noniguanid squamate reptiles. Instead, our findings support the notion that chemosensory traits remain highly conserved.