Reptilian viviparity in cold climates: testing the assumptions of an evolutionary hypothesis

Viviparity (live-bearing) in reptiles often is interpreted as an adaptation to cold climates. This hypothesis relies on (i) body temperatures of gravid females being higher than soil (nest) temperatures; (ii) embryonic development being accelerated by this temperature difference; and (iii) survivorship of hatchlings being increased if eggs hatch before the advent of cold weather in autumn. I gathered data to test these assumptions, using eight species of scincid lizards in a high-elevation area of southeastern Australia. Due to behavioural thermoregulation, body temperatures of gravid lizards average ca. 7°C higher than soil (nest) temperatures. Oviparous female lizards retain eggs in utero for ca. 50% of development. Laboratory studies show that a temperature increase from 17°C (mean nest temperature) to 24°C (mean lizard temperature) reduces incubation periods of eggs by >40 days in heliothermic species, and <20 days in a thigmothermic species. In the field, soil temperatures drop to lethally low levels shortly after the usual time of hatching. Simple calculations show that without the acceleration of development caused by uterine retention, eggs could not hatch prior to the onset of these low temperatures in the field. These results support the major assumptions of the “cold climate hypothesis” for the evolution of reptilian viviparity.     

What limits clutch size? A test of the incubation‐capacity hypothesis in a high‐elevation population of Mountain Bluebirds

Most studies of factors that limit the number of eggs that birds lay have focused on the disadvantages of having too many young to feed. Less attention has been paid to the consequences of having a large number of eggs to incubate. The incubation‐capacity hypothesis proposes that females lay as many eggs as they can effectively incubate. We tested this hypothesis in 2018 in a montane population of Mountain Bluebirds (Sialia currucoides). Most females in this population lay five or six eggs; clutches of seven occur, but are rare. We added eggs to some nests, forcing females to incubate seven eggs, while leaving other nests as controls. Among females completing incubation, those with enlarged clutches hatched as many eggs as did control females, and did so in the same amount of time. This was despite an extended period of unusually cold and often wet weather that occurred when many females were incubating. Our results firmly reject the suggestion that females typically lay no more than six eggs because they cannot effectively heat seven eggs. One or more other factors must limit clutch size. One possible factor is suggested by the fact that during the period of inclement weather, more females with enlarged clutches than control females appeared to abandon nests before completing incubation. Because larger clutches require more energy to incubate, females with seven eggs during energetically stressful conditions could more quickly reach the point where they lack sufficient energy for both incubation and self‐maintenance. Such conditions may occur frequently enough in the montane environment that, on average, laying seven eggs results in reduced lifetime reproductive success.     

Communal nesting under climate change: fitness consequences of higher incubation temperatures for a nocturnal lizard

Communal nesting lizards may be vulnerable to climate warming, particularly if air temperatures regulate nest temperatures. In southeastern Australia, velvet geckos Oedura lesueurii lay eggs communally inside rock crevices. We investigated whether increases in air temperatures could elevate nest temperatures, and if so, how this could influence hatching phenotypes, survival, and population dynamics. In natural nests, maximum daily air temperature influenced mean and maximum daily nest temperatures, implying that nest temperatures will increase under climate warming. To determine whether hotter nests influence hatchling phenotypes, we incubated eggs under two fluctuating temperature regimes to mimic current ‘cold’ nests (mean = 23.2 °C, range 10–33 °C) and future ‘hot’ nests (27.0 °C, 14–37 °C). ‘Hot’ incubation temperatures produced smaller hatchlings than did cold temperature incubation. We released individually marked hatchlings into the wild in 2014 and 2015, and monitored their survival over 10 months. In 2014 and 2015, hot‐incubated hatchlings had higher annual mortality (99%, 97%) than cold‐incubated (11%, 58%) or wild‐born hatchlings (78%, 22%). To determine future trajectories of velvet gecko populations under climate warming, we ran population viability analyses in Vortex and varied annual rates of hatchling mortality within the range 78– 96%. Hatchling mortality strongly influenced the probability of extinction and the mean time to extinction. When hatchling mortality was >86%, populations had a higher probability of extinction (PE: range 0.52– 1.0) with mean times to extinction of 18–44 years. Whether future changes in hatchling survival translate into reduced population viability will depend on the ability of females to modify their nest‐site choices. Over the period 1992–2015, females used the same communal nests annually, suggesting that there may be little plasticity in maternal nest‐site selection. The impacts of climate change may therefore be especially severe on communal nesting species, particularly if such species occupy thermally challenging environments.     

Convergent evolution of embryonic growth and development in the eastern fence lizard (Sceloporus undulatus)

Theory predicts that cold environments will select for strategies that enhance the growth of ectotherms, such as early emergence from nests and more efficient use of resources. We used a common garden experiment to detect parallel clines in rates of embryonic growth and development by eastern fence lizards (Sceloporus undulatus). Using realistic thermal conditions, we measured growth efficiencies and incubation periods of lizards from five populations representing two distinct clades. In both clades, embryos from cold environments (Indiana, New Jersey, and Virginia) grew more efficiently and hatched earlier than embryos from warm environments (Florida and South Carolina). Because eggs from cold environments were larger than eggs from warm environments, we experimentally miniaturized eggs from one population (Virginia) to determine whether rapid growth and development were caused by a greater maternal investment. Embryos in miniaturized eggs grew as efficiently and incubated for the same duration as embryos in unmanipulated eggs. Taken together, our results suggest countergradient variation has evolved at least twice in S. undulatus.     

Impact of increasing temperatures and exposure duration on egg hatch in the hemlock looper,Lambdina fiscellaria

As the growing season is expected to begin earlier under climate change, insects should initiate reproduction several days or weeks earlier than they used to. In eastern Canada, hemlock looper (HL) Lambdina fiscellaria (Guenée) (Lepidoptera: Geometridae) females generally oviposit in September, with eggs entering an obligatory diapause quickly after their deposition. We therefore simulated an early start of the HL reproduction cycle of 2, 4, 6, or 8 weeks to examine the extent to which freshly laid eggs from two populations (island and mainland) can withstand exposure to four temperature conditions (15, 20, 25 °C, or fluctuating temperature in an outdoor insectary), with all treatments ending on 1 September 2007. On this date, half the eggs from each population were immediately incubated at 15 °C, while the rest were stored in an outdoor insectary until their incubation at 15 °C the following spring. In a separate experiment, the effect of temperature on pre‐diapause duration was determined from the number of days required for eggs to change colour after oviposition. The pre‐diapause phase was completed faster as temperature increased. Regardless of incubation date and population, percent hatch decreased significantly after 6‐8 weeks of exposure to 25 °C or in the outdoor insectary. Under most treatments, the odds of dying as pharate larvae increased with exposure duration. When eggs were incubated at 15 °C immediately after treatment, time to hatch and diapause duration remained constant over treatments, except at 25 °C when they both decreased. After 8 weeks of exposure to 15 or 20 °C, eggs transferred outdoors were more likely to hatch precociously than those exposed to 25 °C or insectary conditions. Globally, mortality seemed greater among eggs stored outdoors than among those kept indoors. Most eggs that survived the winter hatched synchronously after incubation in spring. Overall, larger eggs from the island population survived better than smaller eggs from the mainland population.     

Incubation temperature impacts nestling growth and survival in an open‐cup nesting passerine

For oviparous species such as birds, conditions experienced while in the egg can have long‐lasting effects on the individual. The impact of subtle changes in incubation temperature on nestling development, however, remains poorly understood, especially for open‐cup nesting species with altricial young. To investigate how incubation temperature affects nestling development and survival in such species, we artificially incubated American robin (Turdus migratorius) eggs at 36.1°C (“Low” treatment) and 37.8°C (“High” treatment). Chicks were fostered to same‐age nests upon hatching, and we measured mass, tarsus, and wing length of experimental nestlings and one randomly selected, naturally incubated (“Natural”), foster nest‐mate on days 7 and 10 posthatch. We found significant effects of incubation temperature on incubation duration, growth, and survival, in which experimentally incubated nestlings had shorter incubation periods (10.22, 11.50, and 11.95 days for High, Low, and Natural eggs, respectively), and nestlings from the Low treatment were smaller and had reduced survival compared to High and Natural nestlings. These results highlight the importance of incubation conditions during embryonic development for incubation duration, somatic development, and survival. Moreover, these findings indicate that differences in incubation temperature within the natural range of variation can have important carryover effects on growth and survival in species with altricial young.     

The seasonal timing of oviposition in sand lizards (Lacerta agilis): why early clutches are better

We studied a population of sand lizards (Lacerta agilis) near the northern edge of the species' range in coastal Sweden. We captured, marked, released and recaptured 98 adult female lizards over 5 years. Hatchlings from 146 laboratory-incubated clutches (1279 eggs) from field-caught gravid females were measured, weighed, marked and released at the study site. Female sand lizards usually laid only a single clutch of 4 to 15 eggs each year, but varied considerably in the time of year at which they laid their eggs. Oviposition dates shifted between years depending on weather (basking opportunities), but the relative timing of oviposition was consistent within a given female from year-to-year. The first females to oviposit each year were large animals in good physical condition, that had grown rapidly in previous years. “Early” clutches were larger than “later” clutches, had higher hatching success, and tended to have higher post-hatching survival rates. Offspring from early clutches were larger than “later” hatchlings, and differed in body proportions (probably because seasonal changes in maternal temperatures directly modified offspring phenotypes). Overall, our study documents several strong correlates of the timing of oviposition, and suggests that variation in this trait among females has strong fitness consequences, perhaps related to maternal “quality”. The correlations we observed between oviposition date and other traits that have been invoked as determinants of hatchling survival in reptiles (e.g., hatchling size, body shape, opportunities for multiple mating by the mother) suggest that hypotheses advocating simple causal connections between these traits and hatchling success should be viewed with caution.     

Reduced reproductive performance associated with warmer ambient temperatures during incubation in a winter‐breeding,food‐storing passerine

Timing of reproduction can influence individual fitness whereby early breeders tend to have higher reproductive success than late breeders. However, the fitness consequences of timing of breeding may also be influenced by environmental conditions after the commencement of breeding. We tested whether ambient temperatures during the incubation and early nestling periods modulated the effect of laying date on brood size and dominant juvenile survival in gray jays (Perisoreus canadensis), a sedentary boreal species whose late winter nesting depends, in part, on caches of perishable food. Previous evidence has suggested that warmer temperatures degrade the quality of these food hoards, and we asked whether warmer ambient temperatures during the incubation and early nestling periods would be associated with smaller brood sizes and lower summer survival of dominant juveniles. We used 38 years of data from a range‐edge population of gray jays in Algonquin Provincial Park, Ontario, where the population has declined over 50% since the study began. Consistent with the “hoard‐rot” hypothesis, we found that cold temperatures during incubation were associated with larger brood sizes in later breeding attempts, but temperatures had little effect on brood size for females breeding early in the season. This is the first evidence that laying date and temperature during incubation interactively influence brood size in any bird species. We did not find evidence that ambient temperatures during the incubation period or early part of the nestling period influenced summer survival of dominant juveniles. Our findings provide evidence that warming temperatures are associated with some aspects of reduced reproductive performance in a species that is reliant on cold temperatures to store perishable food caches, some of which are later consumed during the reproductive period.     

Reproductive bionomics of the soft tick, Ornithodoros turicata (Acari: Argasidae)

The effects of different temperatures and relative humidities (RHs) were tested on various reproductive parameters of Ornithodoros turicata, an argasid tick that inhabits gopher tortoise burrows in Florida, USA. The pre-oviposition, oviposition and incubation periods of the ticks decreased as temperature increased. These periods were also affected by the RH. The number of eggs oviposited was affected significantly by the combined effect of temperature and RH. Fewer eggs were laid by ticks in the 24°C regimes and the 27°C/95%RH regime compared to those in the other temperature/RH groups. There was an inverse relationship between the number of eggs oviposited and the percentage of hatched larvae that was correlated with the temperature and RH. Ticks reared at 27°C/90%RH and 30°C/90%RH laid more eggs than those reared in the other combinations of temperature and humidity but fewer larvae hatched from these eggs. The reproductive fitness index (RFI) values were highest in females held in the 24°C groups and the 30°C/95%RH group, although significantly more larvae hatched at the lower temperatures. The optimum reproductive conditions for O. turicata under laboratory conditions appear to be 24°C and 90–95%RH. While mating occurred at all temperatures, none of the females laid eggs at 22°C. The ticks may move preferentially to low temperatures when not feeding to remain above the critical equilibrium humidity and/or below the critical metabolic level necessary for prolonged survival. However, most female ticks oviposited after 45 days when moved to 27°C/95%RH. Ornithodoros turicata females may have a limited capability to delay oviposition until an optimal microenvironment for egg deposition can be located in the burrow.     

Reproductive ecology of the jacky dragon (Amphibolurus muricatus): an agamid lizard with temperature‐dependent sex determination

Abstract The jacky dragon, Amphibolurus muricatus (White, ex Shaw 1790) is a medium sized agamid lizard from the southeast of Australia. Laboratory incubation trials show that this species possesses temperature‐dependent sex determination. Both high and low incubation temperatures produced all female offspring, while varying proportions of males hatched at intermediate temperatures. Females may lay several clutches containing from three to nine eggs during the spring and summer. We report the first field nest temperature recordings for a squamate reptile with temperature‐dependent sex determination. Hatchling sex is determined by nest temperatures that are due to the combination of daily and seasonal weather conditions, together with maternal nest site selection. Over the prolonged egg‐laying season, mean nest temperatures steadily increase. This suggests that hatchling sex is best predicted by the date of egg laying, and that sex ratios from field nests will vary over the course of the breeding season. Lizards hatching from eggs laid in the spring (October) experience a longer growing season and should reach a larger body size by the beginning of their first reproductive season, compared to lizards from eggs laid in late summer (February). Adult male A. muricatus attain a greater maximum body size and have relatively larger heads than females, possibly as a consequence of sexual selection due to male‐male competition for territories and mates. If reproductive success in males increases with larger body size, then early hatching males may obtain a greater fitness benefit as adults, compared to males that hatch in late summer. We hypothesize that early season nests should produce male‐biased sex ratios, and that this provides an adaptive explanation for temperature‐dependent sex determination in A. muricatus.     

Erythritol ingestion impairs adult reproduction and causes larval mortality in Drosophila melanogaster fruit flies (Diptera: Drosophilidae)

Previous feeding studies showed the polyalcohol erythritol was toxic when ingested by adult laboratory fruit flies (Drosophila melanogaster). We asked whether erythritol could additionally affect fly population growth either through larval toxicity or through effects on adult reproduction. Females did not avoid laying on food substrates with 1M erythritol; laying rate on 1M erythritol food was similar to control food when females were given free‐choice access. Eggs laid or placed on 0.5 M to 2.5 M erythritol foods hatched at normal rates, suggesting erythritol was not toxic to eggs upon contact. Drosophila melanogaster larvae readily consumed food containing 1 M erythritol, but none of these larvae reached pupation. Longevity of larvae feeding on in 1 M erythritol food was significantly reduced relative to controls, and mean ± SE larval lifespan on erythritol was 1.54 ± 0.10 days (max. = 3 days). Exposing cohorts of second‐instar larvae to food with varying concentrations of erythritol showed the LD50 (at 24 hr) concentration was approximately 0.6 M. Taken together, these results suggest erythritol could be employed in effective larval‐sink baits. Adults flies fed with erythritol produced significantly fewer eggs on days when they fed on 1 M erythritol, and egg production was significantly reduced for one additional day after the adults were moved to control food. These findings suggest erythritol is rapid and effective at temporarily suppressing D. melanogaster reproduction, increasing its potential for use in effective insect population control.     

Relatively low upper threshold temperature in lizards from cool habitats

We used the slender forest skink (Scincella modesta) as a model animal to test for the hypothesis that the upper threshold of incubation temperature is relatively low in lizards using shaded (and thus, cool) habitats. Eight gravid females were collected in early May 2005 from a population in Hangzhou, Zhejiang (eastern China). All females laid a single clutch of 7–13 eggs between mid-May and early June. Eggs were incubated at 24, 28 and 30 (±0.2) °C. None of eggs incubated at 30 °C hatched. Eggs incubated at 24 and 28 °C differed in incubation length but not in hatching success. The incubation length at 24 and 28 °C averaged 22.3 and 20.3 days, respectively. Hatchlings from eggs incubated at 24 and 28 °C did not differ in all examined morphological traits, but hatchlings from eggs incubated at 28 °C performed apparently worse in the racetrack than did their counterparts from eggs incubated at 24 °C. The temperature of 28 °C is close to the upper thermal threshold for successful embryonic development in S. modesta. Compared to other oviparous lizards using open (and thus, warm) habitats, the upper thermal threshold and the range of optimal temperatures for embryonic development are both lower in S. modesta. Our study supports the previous conclusion that species living in thermally different habitats may differ in the upper thermal threshold and the range of optimal temperatures for embryonic development.     

Development of sexual dimorphism in two sympatric skinks with different growth rates

Sexual size dimorphism (SSD) is widespread in animals, especially in lizards (Reptilia: Squamata), and is driven by fecundity selection, male–male competition, or other adaptive hypotheses. However, these selective pressures may vary through different life history periods; thus, it is essential to assess the relationship between growth and SSD. In this study, we tracked SSD dynamics between a “fading‐tail color skink” (blue tail skink whose tail is only blue during its juvenile stage: Plestiodon elegans) and a “nonfade color” tail skink (retains a blue tail throughout life: Plestiodon quadrilineatus) under a controlled experimental environment. We fitted growth curves of morphological traits (body mass, SVL, and TL) using three growth models (Logistic, Gompertz, and von Bertalanffy). We found that both skinks have male‐biased SSD as adults. Body mass has a higher goodness of fit (as represented by very high R² values) using the von Bertalanffy model than the other two models. In contrast, SVL and TL for both skinks had higher goodness of fit when using the Gompertz model. Two lizards displayed divergent life history tactics: P. elegans grows faster, matures earlier (at 65 weeks), and presents an allometric growth rate, whereas P. quadrilineatus grows slower, matures later (at 106 weeks), and presents an isometric growth rate. Our findings imply that species‐ and sex‐specific trade‐offs in the allocation of energy to growth and reproduction may cause the growth patterns to diverge, ultimately resulting in the dissimilar patterns of SSD.     

Sex differences in optimal incubation temperatures in a scincid lizard species

Most theoretical models for the evolution of temperature-dependent sex determination (TSD) rely upon differential fitness of male and female offspring incubated under different thermal regimes. However, there are few convincing data on this topic. We studied incubation effects in a lizard species (Bassiana duperreyi, Scincidae) with genotypic sex determination, so that we could separate effects due to incubation temperatures from those due to offspring gender. We incubated eggs under two different fluctuating-temperature regimes that simulated hot and cold natural nest-sites. The effects of our incubation treatments on phenotypes of the hatchling lizards (morphology and locomotor performance) differed between the sexes. Females emerging from eggs exposed to the “hot nest” treatment (diel cycling, 23–31°C) were larger, and ran faster, than did their sisters from the “cold nest” treatment (16–24°C). Males showed a smaller and less consistent phenotypic response than females. These incubation-induced responses were relatively stable during the first few weeks of life post-hatching, at least in captive lizards maintained under laboratory conditions. These kinds of sex differences in the phenotypic responses of hatchling reptiles to incubation conditions provide a plausible basis for the evolution of temperature-dependent sex determination in reptiles. Received: 07 May 1998 / Accepted: 16 November 1998     

Growth rate, size, and sex ratio of last-laid, last-hatched offspring in the tree swallow Tachycineta bicolor

In tree swallows Tachycineta bicolor, last‐laid eggs typically hatch one to two days after the other eggs in the clutch hatch, putting last‐hatched offspring at a disadvantage when competing for food delivered by parents. We studied the biology of last‐laid, last‐hatched tree swallow offspring over two years in a Wyoming, USA, population. Our first objective was to compare the growth of last‐hatched offspring to that of their earlier‐hatched nestmates. One previous study had suggested that last‐hatched, competitively disadvantaged offspring grow feathers faster than senior nestmates, even at the expense of other aspects of growth. This may allow last‐hatched offspring to fledge with senior nestmates and avoid abandonment by parents. A second objective was to determine the sex of nestlings from last‐laid eggs. If last‐laid eggs typically produce undersized, weak adults that are poor competitors for resources, and if the fitness costs of being undersized/weak are more severe for males than for females, then selection may favour having offspring from last‐laid eggs to be female. In this study, last‐laid eggs hatched in 63 of 66 (94%) nests and hatched last in 93% of cases. At hatching, offspring from last‐laid eggs weighed, on average, 63% as much as their three heaviest nestmates (range: 26–107%). Offspring from last‐laid eggs fledged from 71% of the nests that produced at least one fledgling and apparently starved to death in remaining nests. Last‐hatched offspring who were presumably at a substantial competitive disadvantage (those whose mass at hatching was no more than about 75% of the mean mass of their three heaviest nestmates), gained mass more slowly than their senior nestmates but they eventually attained the same peak mass before fledging. Last‐hatched offspring grew primary feathers more slowly than their senior nestmates although the difference in growth rate was slight (0.2 mm/d) and only marginally significant. As a group, offspring from last‐laid eggs did not differ from offspring from all other eggs in either maximum mass attained before fledging or tarsus length at fledging. This is atypical for species with asynchronous hatching and is possibly the result of another unusual trait: the tendency of parent tree swallows to distribute food equally among young within broods. The sex ratio of offspring from last‐laid eggs did not deviate from 1:1 (22 males, 21 females). Given that last‐hatched eggs do not routinely produce undersized/weak individuals in our study population, there should be little selection on parent females to bias the sex ratio of last‐laid offspring towards females.     

Evolutionary shifts in copepod acid tolerance in an acid-recovering lake indicated by resurrected resting eggs

We employed zooplankton resting eggs to track population-level shifts in acid tolerance over the last century in a boreal shield lake recovering from acidification. Shifts in mean and variance of ecological tolerances of species that occupy ecosystems recovering from anthropogenic stress are important to consider because of their potential to influence eco-evolutionary dynamics at community and ecosystem levels. In a laboratory experiment, we compared juvenile survival of Leptodiaptomus minutus copepods hatched from resting eggs from three time periods (80- to 100-year- old: pre-industrial, 20- to 50-year- old: lake acidification, and 8- to 10-year- old: recovery of lake-water back to pH ≥ 6.0) under several pH treatments. Mitochondrial DNA was used to confirm species identity and to test for population bottlenecks as a possible mechanism to explain our results. We expected that nauplii hatched from eggs deposited prior to industrialization (lake-water pH ≈ 6.0) and from the period of pH recovery (lake-water pH ≥ 6.0) would have lower mean and more variable survival at acidic pH compared to nauplii hatched from the period of peak lake acidification (lake-water pH ≈ 4.7). Our results, which are likely a combination of both genetic and environmental effects, suggest support for this hypothesis. Nauplii hatched from eggs deposited during the period of acidification in George Lake had reduced variation in pH tolerance compared to the recovery period. This was likely driven by strong selection rather than genetic drift because we found no evidence of a population bottleneck. However, we could not detect differences in the variance of naupliar survival between pre-industrial and acidic time periods. Trends in mean naupliar survival from different time periods matched findings from other field-based studies that detected a relationship between lake acidification history and acid tolerance in L. minutus.     

Behavior and season affect crayfish detection and density inference using environmental DNA

Although the presence/absence of aquatic invertebrates using environmental DNA (eDNA) has been established for several species, inferring population densities has remained problematic. The invasive American signal crayfish, Pacifastacus leniusculus (Dana), is the leading cause of decline in the UK's only native crayfish species, Austropotamobius pallipes (Lereboullet). Methods to detect species at low abundances offer the opportunity for the early detection, and potential eradication, of P. leniusculus before population densities reach threatening levels in areas occupied by A. pallipes. Using a factorial experimental design with aquaria, we investigated the impacts of biomass, sex ratio, and fighting behavior on the amount of eDNA released by P. leniusculus, with the aim to infer density per aquarium depending on treatments. The amount of target eDNA in water samples from each aquarium was measured using the quantitative Polymerase Chain Reaction. We show that the presence of eggs significantly increases the concentration of crayfish eDNA per unit of mass, and that there is a significant relationship between eDNA concentration and biomass when females are egg‐bearing. However, the relationship between crayfish biomass and eDNA concentration is lost in aquaria without ovigerous females. Female‐specific tanks had significantly higher eDNA concentrations than male‐specific tanks, and the prevention of fighting did not impact the amount of eDNA in the water. These results indicate that detection and estimate of crayfish abundance using eDNA may be more effective while females are ovigerous. This information should guide further research for an accurate estimation of crayfish biomass in the field depending on the season. Our results indicate that detection and quantification of egg‐laying aquatic invertebrate species using eDNA could be most successful during periods when eggs are developing in the water. We recommend that practitioners consider the reproductive cycle of target species when attempting to study or detect aquatic species using eDNA in the field.     

Maternal and environmental influences on egg size and juvenile life‐history traits in Pacific salmon

Life‐history traits such as fecundity and offspring size are shaped by investment trade‐offs faced by mothers and mediated by environmental conditions. We use a 21‐year time series for three populations of wild sockeye salmon (Oncorhynchus nerka) to test predictions for such trade‐offs and responses to conditions faced by females during migration, and offspring during incubation. In years when their 1100 km upstream migration was challenged by high water discharges, females that reached spawning streams had invested less in gonads by producing smaller but not fewer eggs. These smaller eggs produced lighter juveniles, and this effect was further amplified in years when the incubation water was warm. This latter result suggests that there should be selection for larger eggs to compensate in populations that consistently experience warm incubation temperatures. A comparison among 16 populations, with matching migration and rearing environments but different incubation environments (i.e., separate spawning streams), confirmed this prediction; smaller females produced larger eggs for their size in warmer creeks. Taken together, these results reveal how maternal phenotype and environmental conditions can shape patterns of reproductive investment and consequently juvenile fitness‐related traits within and among populations.     

Nesting ecology of a naturalized population of Mallards Anas platyrhynchos in New Zealand

Investigating the reproductive ecology of naturalized species provides insights into the role of the source population's characteristics vs. post‐release adaptation that influence the success of introduction programmes. Introduced and naturalized Mallards Anas platyrhynchos are widely established in New Zealand (NZ), but little is known regarding their reproductive ecology. We evaluated the nesting ecology of female Mallards at two study sites in NZ (Southland and Waikato) in 2014–15. We radiotagged 241 pre‐breeding females with abdominal‐implant transmitters and measured breeding incidence, nesting chronology and re‐nesting propensity. We monitored 271 nests to evaluate nest survival, clutch and egg size, egg hatchability and partial clutch depredation. Breeding incidence averaged (mean ± se) 0.91 ± 0.03, clutch size averaged 9.9 ± 0.1 eggs, 94 ± 2% of eggs hatched in successful nests, partial depredation affected 6 ± 1% of eggs in clutches that were not fully destroyed by predators, and re‐nesting propensity following failure of nests or broods was 0.50 ± 0.003. Nesting season (first nest initiated to last nest hatched) lasted 4.5 months and mean initiation date of first detected nest attempts was 28 August ± 3.3 days. Smaller females were less likely to nest, but older, larger or better condition females nested earlier, re‐nested more often and laid larger clutches than did younger, smaller or poorer condition females. Younger females in Southland had higher nest survival; cumulative nest survival ranged from 0.25 ± 0.007 for adult females in Waikato to 0.50 ± 0.007 for yearling females in Southland. Compared with Mallards in their native range, the nesting season in NZ was longer, clutches and eggs were larger, and nest survival was generally greater. Different predators and climate, introgression with native heterospecifics and/or the sedentary nature of Mallards in NZ may have contributed to these differences.     

Chemosensory enrichment as a simple and effective way to improve the welfare of captive lizards

Environmental enrichment has proven to be a useful and effective welfare tool in order to evaluate and enhance the well‐being of captive animals, but only when it is based on detailed knowledge of each species' natural behaviour. Chemoreception is fundamental to many aspects of reptilian biology; however, sensory enrichment with chemical stimuli has rarely been applied to reptiles. In this study, we evaluate the use of chemosensory enrichment as a method to enhance the welfare of Podarcis liolepis. For seven weeks, we exposed field‐caught males to scents from donor conspecific males collected on pieces of filter paper (i.e., “enriched” group, n = 18), and compared their behaviour to that of control males provided with unscented pieces of filter paper (n = 18). We measured the occurrence of normal (e.g., locomotion) and abnormal (escape attempts) behaviours each day for three weeks. In addition, we conducted two exploration tests and a visual barrier test. Compared to controls, enriched lizards showed a consistent long‐term decrease (29%–38%) in the occurrence of escape attempts. During exploration tests, enriched lizards spent less time performing escape attempts and devoted more time to perching than controls. As expected, both control and enriched lizards showed a reduction of time in locomotion and an increase in the time spent perching between the first and second exploration test, but these changes were significantly more pronounced for enriched animals. Taken together, our results suggest improved welfare of enriched animals, as they spent less time engaging in abnormal behaviours, more time in normal behaviours, and showed signs of faster habituation to a novel environment. Chemosensory enrichment is a relatively simple enrichment strategy that could potentially be applied to improve the welfare of a wide range of captive lizards, and reptiles at large.