Seasonal Dissociation in Fossorial Activity between the Llanos' Frog Populations as a Survival Strategy in Arid Subtropical Environments
Among amphibians, the fossorial habit is an evolutionary strategy to maintain their niches along space and time, avoiding hostile climate conditions. The fossorial frog Lepidobatrachus llanensis has evolved in temperate regions, adapted and distributed in arid subtropical environments, and is divided into two well-defined and isolated populations (northern and southern). In this study, we analyze if these two populations have adjusted their activity patterns (i.e., feeding and reproduction) as a strategy to retain their ecological niche characteristics along a semiarid latitudinal gradient. We modeled and characterized the ecological niches via Euclidean distance to the ecological niche centroid of the entire species under the false premise that the two populations are equally active throughout the year (i.e., annual niche). Then, we repeated the exercise considering the niches for the two populations (by estimating their real seasonal niche activity). We also performed comparisons between both populations via a similarity test. Our results suggest that both populations are active in similar climatic conditions but in different (dissociated) temporalities, suggesting that seasonal activity in fossorial species is a strategy to conserve their climatic niche in two different geographical areas across the year. Entre los anfibios, el hábito fosorial es una estrategia evolutiva para mantener sus nichos a lo largo del espacio y el tiempo, evitando condiciones climáticas hostiles. La rana fosorial Lepidobatrachus llanensis ha evolucionado en regiones templadas, adaptada y distribuida en ambientes áridos subtropicales y posee dos poblaciones aisladas y bien diferenciadas (norte y sur). En este estudio analizamos si estas dos poblaciones han ajustado sus patrones de actividad (i.e., alimentación y reproducción) como una estrategia para retener sus características de nicho a través de un gradiente latitudinal semi-árido. Modelamos y caracterizamos su nicho ecológico, a través de distancias Euclidianas hacia el centroide de su nicho ecológico de la especie completa, bajo la falsa premisa de que las dos poblaciones son igualmente activas a lo largo de todo el año (i.e., nicho anual). Posteriormente repetimos el ejercicio considerando los nichos de las dos poblaciones (a través de estimar la actividad real de sus nichos estacionales). Llevamos a cabo además comparaciones entre ambas poblaciones a través de una prueba de similitud. Nuestros resultados sugieren que ambas poblaciones están activas en condiciones climáticas similares, pero en temporadas diferentes (disociadas), sugiriendo que la actividad estacional en especies fosoriales es una estrategia para conservar sus nichos climáticos en dos diferentes áreas a lo largo del año.ABSTRACT
RESUMEN
Geographic distribution of the localities of Lepidobatrachus llanensis. Gray dots correspond to the northern population and white dots to the southern population. Gray polygon represents the area of accessibility (M) used for model calibration.
Temporal characterization of the activity records (blue lines) of both populations in all surveyed localities (orange lines) along all months of the year. See Materials and Methods section for a detailed description.
Localities of Lepidobatrachus llanensis at different moments of the year: (A) Filled temporary pond during the wet season. (B) Dry temporary pond during the dry season.
(A) Relationship between Euclidean distances to the niche centroid vs. the number of records (in percentage) considering annual and seasonal (northern and southern) approaches. The geographic representation of this relationship is shown for (B) seasonal, and (C) annual approaches.
Comparisons of northern and southern populations' niches of Lepidobatrachus llanensis, using the niche-overlap test proposed by Broennimann et al. (2012) under annual (left) and seasonal (right) approaches. In upper graphs, solid colors represent the niche of the species (northern in red, southern in green, and blue in the intersection) along the two first axes of the PCA; gray shading represents the density of the occurrences of the species; solid and dashed contour lines illustrate, respectively, 100% and 50% of the available environmental background for the northern (red) and southern (green) niches. Lower histograms represent the frequency of simulated niche overlaps (gray bars), and the red diamond, the observed niche overlap D between the two ranges (southern and northern) for the annual (left) and seasonal (right) background.
Overlap of each variable composing the niche, between northern (red) and southern (green) populations, compared annually (left), and seasonally (right).
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