Contrasting Patterns of Movement across Life Stages in an Insular Iguana Population

Locating Nesting Sites for Critically Endangered Galápagos Pink Land Iguanas (Conolophus marthae)

Invasive alien species control is recognized worldwide as a priority action to preserve global biodiversity. However, a lack of general life history knowledge for threatened species can impede the effectiveness of conservation actions. Galápagos pink land iguanas (Conolophus marthae) are endemic to Wolf Volcano, Galápagos, Ecuador. These iguanas are threatened by invasive alien species, particularly feral cats, that may affect their small population size. To guarantee the long-term survival of C. marthae, the Galápagos National Park Directorate is considering, along with an ongoing campaign of feral cat control, the implementation of a head-start program. However, the success of this management strategy necessarily relies on the identification of pink iguana nesting grounds, which were still unknown at the onset of this study. We modeled the movement patterns of male and female iguanas during the reproductive season, using location data collected from custom-made remote tracking devices installed on adult pink iguanas in April 2021. We first calculated for each individual the vector of distances from its starting location, which was defined as net displacement. We then used net displacement as the response variable in a generalized additive mixed model with day of the year as the predictor. Based on the hypothesis that males and females may behaviorally differ after mating, we looked for female-specific migratory behavior suggesting females were moving toward nesting areas. The results obtained confirmed our hypothesis, as females exhibited a distinct migratory behavior, reaching a small plateau area inside of Wolf Volcano's caldera and ca. 400 m below the volcano's northern rim. Moreover, once inside the caldera, females displayed a more aggregated distribution pattern. The movement data obtained allowed Galápagos National Park rangers to locate individual pink iguana nests and subsequently to sight and collect the first observed hatchlings of the species. This work constitutes a necessary baseline to perform dedicated studies of pink iguana nests and emerging hatchling iguanas, which is an essential step toward the development of an effective head-start program.

Comparative exploratory movements of two terrestrial isopods (suborder: Oniscidea), in response to humidity and availability of food

Unfavourable conditions within familiar environments may prompt organisms to make forays into other habitats, at least temporarily. This behaviour is in turn linked to key demographic processes such as immigration, emigration, and eventually, metapopulation dynamics. How such movements are triggered by environmental conditions (much less their interaction effects) has rarely been experimentally tested. To address this, we examined how environmental conditions (3 levels of food and 3 levels of humidity) within a microcosm affect the movements of two species of isopods (Armadillidium vulgare and Porcellio scaber) out of their familiar habitat. We used web-camera checkpoints to record the movements of individually marked animals as they conducted forays along corridors that lead to new, unused habitats. Thirty-six trials were run in total for each species, with each trial involving 16 animals (8 ♂♂, 8 ♀♀). Relatively unfavourable conditions of low humidity, low food levels, and their interaction prompted changes to all the foray metrics we measured. However, different levels of mobility and tolerance to desiccation between the two species also appeared linked to the degree of responses, e.g., Porcellio demonstrated a greater tendency to depart from familiar habitat under low humidity, possibly due to their superior mobility and greater susceptibility to desiccation. This study improves our understanding of how different environmental conditions act in concert to affect the exploratory movements away from familiar habitat, and how these responses differ even for closely-related species.

Conditional female strategies influence hatching success in a communally nesting iguana

The decision of females to nest communally has important consequences for reproductive success. While often associated with reduced energetic expenditure, conspecific aggregations also expose females and offspring to conspecific aggression, exploitation, and infanticide. Intrasexual competition pressures are expected to favor the evolution of conditional strategies, which could be based on simple decision rules (i.e., availability of nesting sites and synchronicity with conspecifics) or on a focal individual's condition or status (i.e., body size). Oviparous reptiles that reproduce seasonally and provide limited to no postnatal care provide ideal systems for disentangling social factors that influence different female reproductive tactics from those present in offspring-rearing environments. In this study, we investigated whether nesting strategies in a West Indian rock iguana, Cyclura nubila caymanensis, vary conditionally with reproductive timing or body size, and evaluated consequences for nesting success. Nesting surveys were conducted on Little Cayman, Cayman Islands, British West Indies for four consecutive years. Use of high-density nesting sites was increasingly favored up to seasonal nesting activity peaks, after which nesting was generally restricted to low-density nesting areas. Although larger females were not more likely than smaller females to nest in high-density areas, larger females nested earlier and gained access to priority oviposition sites. Smaller females constructed nests later in the season, apparently foregoing investment in extended nest defense. Late-season nests were also constructed at shallower depths and exhibited shorter incubation periods. While nest depth and incubation length had significant effects on reproductive outcomes, so did local nest densities. Higher densities were associated with significant declines in hatching success, with up to 20% of egg-filled nests experiencing later intrusion by a conspecific. Despite these risks, nests in high-density areas were significantly more successful than elsewhere due to the benefits of greater chamber depths and longer incubation times. These results imply that communal nest sites convey honest signals of habitat quality, but that gaining and defending priority oviposition sites requires competitive ability.