James Baxter-Gilbert

Biological invasions provide unique opportunities to examine how populations cope with rapid ecological change, as well as the influence of human activity on our natural world. The island of Newfoundland, Canada, has no native amphibians; however, five species have established non-native populations, including one caudatan, the Eastern Red-backed Salamander ( Plethodon cinereus ). We posit that this salamander’s successful colonisation may have been mediated by dietary shifts that allowed them to capitalize on a greater variety of prey, as well as by exploiting pre-existing invasive prey communities – both these mechanisms could limit the likelihood of competitive exclusion and promote establishment in a novel environment. To examine this, we identified stomach contents of Newfoundland Eastern Red-backed salamanders, characterised the prey as native or invasive, and compared the dietary composition of the invasive population to that of conspecifics in the native range through a systematic literature review. As predicted, the invasive salamander population’s diet is more generalised (i.e., a broader dietary niche) than the native salamanders, and invasive invertebrates comprised two thirds of the volume of prey eaten by invasive salamanders. Our research provides insight into the Niche Breadth Invasion Hypothesis as well as the Invasional Meltdown Hypothesis, which are mechanisms that may have allowed this species to establish a population in an island ecosystem. Furthermore, our research suggests that prior invasions of a diverse invertebrate community to Newfoundland may have bolstered the invasive potential of this novel, non-native salamander.

Background: Urbanisation can negatively impact biodiversity, often resulting in smaller and more isolated populations—which can be particularly detrimental for habitat specialists. Yet, under the right ecological conditions, urbanised greenspaces can also act as refugia for remnant populations to persist. The Four-toed Salamander ( Hemidactylium scutatum ) is an example of a macrohabitat specialist; it is an amphibian which relies specifically on habitat with bogs/fens and adjacent upland forests. In New Brunswick, Canada, this salamander is presumed to be critically imperilled as it had previously only been observed in a single location, a protected national park. A second population, however, was recently discovered within an urbanised greenspace in Riverview, New Brunswick. Notably, this area is enveloped by anthropogenic landscape features ( e.g. , roads, parking lots, housing, businesses), which demonstrates how this species can also occur in more urbanised areas. Our study aims to understand the population ecology of Four-toed Salamanders at this newly described site and investigate how its habitat use allows it to persist in an area with strong anthropogenic disturbance. Methods: We estimated the current relative abundance and density, and quantified the demographics, of Four-toed Salamanders at the Riverview site, while also testing to see if these salamanders favoured specific microhabitats within both fen and upland forest habitats. We contrasted a wide range of suitable environmental variables ( e.g. , substrate temperature, acidity, canopy cover, humidity, and plant percent coverage) between locations containing a salamander to nearby, unoccupied locations. Results: We found a total of 67 salamanders across all surveys, which translates to a conservative relative population density estimate of 2.12 individuals/ha. We observed few differences in microhabitats between where salamanders were seen and random locations, which suggests that suitable microhabitats were not limited for these amphibians at this site. These differences were that salamanders preferred higher slopes within moss hummocks in fens, cooler substrates in the forest, and the presence of woody debris in the forest. Discussion & Conclusion: Our study provides key insights into the habitat characteristics of Four-toed Salamanders at the northern extent of their range, a species with a cryptic lifestyle that is widely considered to be a macrohabitat specialist. By quantifying the ecological features of an urban habitat being used by Four-toed Salamanders in New Brunswick, we expand the types of ecosystems conservation biologists and wildlife managers should consider viable when conducting additional surveys and assessments for this species. This study increases our knowledge about the niche of an amphibian whose conservation and protection in New Brunswick, and more broadly in Canada, is hindered by a lack of foundational natural history data.

Parental care can be seen across a wide variety of taxa, including arachnids, where varying degrees of maternal investment into offspring care can be seen. While some forms of maternal care, like egg-sac guarding, carrying young, and defending against predators, are common in spiders, more intensive behavior, like the direct provisioning of energetic resources to offspring, is less commonly observed. Provisioning behavior has been recorded in ∼0.001% of spider species to date, half of which are in the Family Theridiidae. Here, we present a set of observations for another theridiid spider, Enoplognatha ovata (Candy-striped Spider), engaged in provisioning behavior. Our captive observations of maternal behavior recorded 3 instances of prey items being captured and presented to young spiderlings by the mother, who, herself, did not appear to partake in feeding. We discuss potential drivers of this behavior and how it may play a role within the invasion success of this species in North America.

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A prominent feature of the modern era is the increasing spread of invasive species, particularly within island and urban ecosystems, and these occurrences provide valuable natural experiments by which evolutionary and invasion hypotheses can be tested. In this study, we used the invasion route of guttural toads (Sclerophrys gutturalis) from natural-native and urban-native populations (Durban, South Africa) to their urban-invasive and natural-invasive populations (Mauritius and Réunion) to determine whether phenotypic changes that arose once the toads became urbanized in their native range have increased their invasive potential before they were transported (i.e., prior adaptation) or whether the observed changes are unique to the invasive populations. This urban/natural by native/invasive gradient allowed us to examine differences in guttural toad morphology (i.e., body size, hindlimb, and hindfoot length) and performance capacity (i.e., escape speed, endurance, and climbing ability) along their invasion route. Our findings indicate that invasive island populations have reduced body sizes, shorter limbs in relation to snout-vent length, decreased escape speeds, and decreased endurance capacities that are distinct from the native mainland populations (i.e., invasion-derived change). Thus, these characteristics did not likely arise directly from a pre-transport anthropogenic “filter” (i.e., urban-derived change). Climbing ability, however, did appear to originate within the urban-native range and was maintained within the invasive populations, thereby suggesting it may have been a prior adaptation that provided this species with an advantage during its establishment in urban areas and spread into natural forests. We discuss how this shift in climbing performance may be ecologically related to the success of urban and invasive guttural toad populations, as well as how it may have impacted other island-derived morphological and performance phenotypes.

The island of Newfoundland has no native amphibian taxa, although six species of Anura (i.e., frogs and toads) have been introduced since European colonisation, four of which have established self-sustaining populations. Here, we document Eastern Red-backed Salamander (Plethodon cinereus) on Newfoundland for the first time, in what appears to be a self-sustaining population near Conception Bay South. This is the first species of Caudata (i.e., newts and salamanders) to have been introduced to the island, as well as the first occurrence of Eastern Red-backed Salamander establishing a population outside its native range. The impact that this non-native species might have on forest ecosystems on Newfoundland is unclear and further study is required to determine whether eradication of the species from Newfoundland is necessary or feasible.

Animals are increasingly challenged to respond to novel or rapidly changing habitats due to urbanization and/or displacement outside their native range by humans. Behavioral differences, such as increased boldness (i.e., propensity for risk-taking), are often observed in animals persisting in novel environments; however, in many cases, it is unclear how these differences arise (e.g., through developmental plasticity or evolution) or when they arise (i.e., at what age or developmental stage). In the Guttural Toad (Sclerophrys gutturalis), adult urban toads from both native and invasive ranges are bolder than conspecifics in natural habitats. Here, we reared Guttural Toad tadpoles in a common garden experiment, and tested for innate differences in boldness across their development and between individuals whose parents and lineage came from rural-native, urban-native, and urban-invasive localities (i.e., origin populations). Tadpoles did not differ in their boldness or in how their boldness changed over ontogeny based on their origin populations. In general, tadpoles typically became less bold as they aged, irrespective of origin population. Our findings indicate that differences in boldness in free-living adult Guttural Toads are not innate in the tadpole stage and we discuss three possible mechanisms driving phenotypic divergence in adult boldness for the focus of future research: habitat-dependent developmental effects on tadpole behavior, decoupled evolution between the tadpole and adult stage, and/or behavioral flexibility, learning, or acclimatization during the adult stage. Significance statement To determine if animals can persist in urban areas or become invasive outside their native ranges, it is important to understand how they adapt to life in the city. Our study investigates if differences in boldness that have been found in adult Guttural Toads (Sclerophrys gutturalis) represent heritable differences that can also be found in early life stages by rearing tadpoles from eggs in a common garden experiment. We did not find any differences in boldness among tadpoles from rural-native, urban-native, and urban-invasive origin populations. Our findings suggest that differences in boldness are not innate and/or that boldness is a behavioral trait that is decoupled between the tadpole and the adult stage.

Hatching/birthing asynchrony, when siblings emerge at least 12 h apart, is thought to be a significant driver of phenotypic variation and group cohesion that is commonly reported in invertebrates and birds, but rarely in squamates. We examined birthing asynchrony in African cordylid lizards (Cordylidae), a clade characterized by a wide range of sociality (a hypothesized evolutionary driver of this unique phenomenon). We monitored parturition from wild‐caught mothers from four species, which vary in their conspecific grouping behaviour. In two species, most litters were born asynchronously, over a maximum of 3–4 days respectively. The other two cordylids also exhibited asynchronous birth in all litters with more than one offspring, although this was not applicable for most litters because there was a prevalence of singleton litters. Our study uncovered birthing asynchrony in a novel taxonomic group, which suggests it evolved convergently in at least two social lizard clades from different continents. Furthermore, the function of birthing asynchrony and limiting litter size to a single offspring may be similar in social animals. We discuss the potential significance of this rare phenomenon in this disparate taxon, and compare it with other more well‐studied taxa, in order to guide future research directions.

Cities are focal points of introduction for invasive species. Urban evolution might facilitate the success of invasive species in recipient urban habitats. Here we test this hypothesis by rearing tadpoles of a successful amphibian urban coloniser and invader in a common garden environment. We compared growth rate, morphological traits, swimming performance, and developmental rate of guttural toad tadpoles (Sclerophrys gutturalis) from native rural, native urban, and non-native urban habitats. By measuring these traits across ontogeny, we were also able to compare divergence across different origins as the tadpoles develop. The tadpoles of non-native urban origin showed significantly slower developmental rate (e.g., the proportion of tadpoles reaching Gosner stage 31 or higher was lower at age 40 days) than tadpoles of native urban origin. Yet, tadpoles did not differ in growth rate or any morphological or performance trait examined, and none of these traits showed divergent ontogenetic changes between tadpoles of different origin. These findings suggest that prior adaptation to urban habitats in larval traits likely does not play an important role in facilitating the invasion success of guttural toads into other urban habitats. Instead, we suggest that evolutionary changes in larval traits after colonization (e.g., developmental rate), together with decoupling of other traits and phenotypic plasticity might explain how this species succeeded in colonising extra-limital urban habitats.