Testing the Fitness Consequences of the Thermoregulatory and Parental Care Models for the Origin of Endothermy

The origin of endothermy is a puzzling phenomenon in the evolution of vertebrates. To address this issue several explicative models have been proposed. The main models proposed for the origin of endothermy are the aerobic capacity, the thermoregulatory and the parental care models. Our main proposal is that to compare the alternative models, a critical aspect is to determine how strongly natural selection was influenced by body temperature, and basal and maximum metabolic rates during the evolution of endothermy. We evaluate these relationships in the context of three main hypotheses aimed at explaining the evolution of endothermy, namely the parental care hypothesis and two hypotheses related to the thermoregulatory model (thermogenic capacity and higher body temperature models). We used data on basal and maximum metabolic rates and body temperature from 17 rodent populations, and used intrinsic population growth rate (Rmax) as a global proxy of fitness. We found greater support for the thermogenic capacity model of the thermoregulatory model. In other words, greater thermogenic capacity is associated with increased fitness in rodent populations. To our knowledge, this is the first test of the fitness consequences of the thermoregulatory and parental care models for the origin of endothermy

Comparative Energetics of the Subterranean Ctenomys Rodents: Breaking Patterns

Subterranean mammals show lower mass independent basal metabolic rates (BMR), and several competing hypotheses were suggested to explain how microenvironmental conditions and underground life affect subterranean mammalian energetics. Two of these are the thermal-stress and the cost-of- burrowing hypotheses. The thermal-stress hypothesis posits that a lower massindependent BMR reduces overheating in burrows where convective and evaporative heat loss is low, whereas the cost-of- burrowing hypothesis states that a lower mass-independent BMR may compensate for the high energy expenditure of digging. In this paper we assessed the relationship between BMR of Ctenomys and environmental variables through conventional statistics as well independent contrasts. Moreover, we tested both, thermal-stress and cost of burrowing hypotheses at an interspecific level in a very homogenous genus of subterranean rodents, the South American genus Ctenomys. We compared species from different geographic localities with contrasting habitat conditions. We measured BMR through open flow respirometry. After conventional as well independent contrast analyses, our results support neither the thermal stress nor the cost of burrowing hypotheses. We observed that only body mass affect the variability in BMR. No contrasting climatic and soil conditions, habitat productivity, or net primary productivity were correlated with BMR variability. We suggested that since BMR and maximum metabolic rates (MMR) are correlated, low BMR´s among Ctenomys species could be also determined by factors that affect MMR rather BMR.Fil: Luna, Facundo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; ArgentinaFil: Antenucci, Carlos Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; ArgentinaFil: Bozinovic, Francisco. Pontificia Universidad Católica de Chile; Chil

How do ectotherms perform in cold environments? Physiological and life-history traits in an Andean viviparous lizard

Material complementario: https://www.frontiersin.org/articles/10.3389/fevo.2022.974968/full#supplementary-materialBoth the mean and the variation in environmental temperature are increasing globally. Indeed, the predicted increases in temperature range from 2 to 4°C in the next 50 years. Ectotherms control body temperature by means of behavior selecting microsites with different temperatures, which makes them more susceptible to changes in climate. Nevertheless, lizards living in high mountain environments have developed several mechanisms to inhabit and colonize variable environments with extreme temperatures. These mechanisms include a high metabolism to be active at lower temperatures and viviparity to improve embryonic development. Despite behavioral thermoregulation acting as a buffer to changes in environmental temperature, other traits such as lifehistory traits may be less flexible. Consequently, in an attempt to understand how lizards cope with harsh habitats, we evaluated some physiological traits and responses of females of Liolaemus bellii from two contrasting slope sites with differences in environmental temperature and humidity, but at the same altitude in the southern Andes range. We collected pregnant females from opposite slopes and maintained them until parturition in a commongarden experiment. Females from the south-facing slope (S-slope) had higher preferred body temperature (Tpref) values before and after parturition and exhibited higher daily energy expenditure before parturition. Nevertheless, no difference in Tpref was shown by their offspring, suggesting a developmental plastic response or adaptation to lower environmental temperature. For instance, the higher metabolism during pregnancy could be associated with a shorter activity period on the snowy S-slope. Additionally, females from the S-slope had larger kidneys and gave birth later than N-slope females, likely due to developmental plasticity or genetic differentiation. How fixed these traits are, in individuals from the contrasting slopes, will determine the response capacity of the L. bellii population to climate change

Fluctuating thermal environments and time-dependent effects on fruit fly egg-hatching performance

Organismal performance in a changing environment is dependent on temporal patterns and duration of exposure to thermal variability. We experimentally assessed the time-dependent effects of thermal variability (i.e., patterns of thermal exposure) on the hatching performance of Drosophila melanogaster. Flies were collected in central Chile and maintained for four generations in laboratory conditions. Fourth generation eggs were acclimated to different thermal fluctuation cycles until hatching occurred. Our results show that the frequency of extreme thermal events has a significant effect on hatching success. Eggs exposed to 24 hr cycles of thermal fluctuation had a higher proportion of eggs that hatched than those acclimated to shorter (6 and 12 hr) and longer cycles (48 hr). Furthermore, eggs subjected to frequent thermal fluctuations hatched earlier than those acclimated to less frequent thermal fluctuations. Overall, we show that, egg-to-adult viability is dependent on the pattern of thermal fluctuations experienced during ontogeny; thus, the pattern of thermal fluctuation experienced by flies has a significant and until now unappreciated impact on fitness.Fil: Cavieres Parada, Grisel Beatriz. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Investigaciones de las Zonas Áridas. Provincia de Mendoza. Instituto Argentino de Investigaciones de las Zonas Áridas. Universidad Nacional de Cuyo. Instituto Argentino de Investigaciones de las Zonas Áridas; Argentina. Pontificia Universidad Católica de Chile; ChileFil: Bogdanovich, José M.. Pontificia Universidad Católica de Chile; Chile. Universidad Santo Tomas; ArgentinaFil: Toledo, Paloma. Pontificia Universidad Católica de Chile; ChileFil: Bozinovic, Francisco. Pontificia Universidad Católica de Chile; Chil

Animals eat what they should not: why do they reject our foraging models

ABSTRACT In this commentary we identify several conditions in which the conventional criteria used by optimal foraging theory are insufficient to explain food choice in animals. We also suggest reasons why these criteria are insufficient and provide the ingredients needed to fully account for the observed results. We illustrate the role of: (I) digestive physiology and subtle chemical dietary differences on food choice: (2) micronutrients and animal's physiology on food selection; (3) dietary associative effects on food ingestion and nutrients assimilation, and finally (4) we ask and analyse why do animals feed on poor dietary items. We propose a shift from the simple energy-based models of foraging to more mechanistic approaches. This shift necessitates that we attempt to understand the role that physiological complexity has on an animal's behavior. Key words: foraging behavior. food chemistry, animal physiology. RESUMEN En este comentario identificamos una serie de condiciones por las cuales Ios criterios convencionales usados por la teoria de forrajeo 6ptimo son insuficientes para explicar la selecci6n de alimento que realizan Ios animales. Sugerimos además las razones por las cuales estos criterios son insuficientes y proponemos Ios ingredientes necesarios para dar cuenta de Ios resultados observados. llustramos el efecto de: (I) la fisiologia digestiva y l as diferencias qui micas dietarias sutiles sobre las preferencias alimentarias: (2) los micronutrientes y la fisiologia de Ios animales sobre la selecci6n de alimento: (3) !as dietas mixtas sobre la ingestion de alimento y la asimilaci6n de nutrientes, y finalmente (4) nos preguntamos y analizamos par qué Ios animales se alimentan de itemes dietarios pobres. Proponemos un cambio desde los modelos de forrajeo simples basados en energia a aproximaciones más mecanicistas: esto requiere que intentemos entender el rol que posee la complejidad fisiol6gica sabre la conducta animal. Palabras clave: conducta de alimentaci6n, quimica del alimento, fisiologia animal

Transgenerational and within-generation plasticity shape thermal performance curves

Thermal performance curves (TPCs) compute the effects of temperature on the performance of ectotherms and are frequently used to predict the effect of environmental conditions and currently, climate change, on organismal vulnerability and sensitivity. Using Drosophila melanogaster as an animal model, we examined how different thermal environments affected the shape of the performance curve and their parameters. We measured the climbing speed as a measure of locomotor performance in adult flies and tested the ontogenetic and transgenerational effects of thermal environment on TPC shape. Parents and offspring were reared at 28 ± 0ºC (28C), 28 ± 4ºC (28V), and 30 ± 0ºC (30C). We found that both, environmental thermal variability (28V) and high temperature (30C) experienced during early ontogeny shaped the fruit fly TPC sensitivity. Flies reared at variable thermal environments shifted the TPC to the right and increased heat tolerance. Flies held at high and constant temperature exhibited lower maximum performance than flies reared at the variable thermal environment. Furthermore, these effects were extended to the next generation. The parental thermal environment had a significative effect on TPC and its parameters. Indeed, flies reared at 28V whose parents were held at a high and constant temperature (30C) had a lower heat tolerance than F1 of flies reared at 28C or 28V. Also, offspring of flies reared at variable thermal environment (28V) reached the maximum performance at a higher temperature than offspring of flies reared at 28C or 30C. Consequently, since TPC parameters are not fixed, we suggest cautiousness when using TPCs to predict the impact of climate change on natural populations.Fil: Cavieres Parada, Grisel Beatriz. Pontificia Universidad Católica de Chile; Chile. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Investigaciones de las Zonas Áridas. Provincia de Mendoza. Instituto Argentino de Investigaciones de las Zonas Áridas. Universidad Nacional de Cuyo. Instituto Argentino de Investigaciones de las Zonas Áridas; ArgentinaFil: Alruiz, José M.. Pontificia Universidad Católica de Chile; ChileFil: Medina, Nadia R.. Pontificia Universidad Católica de Chile; ChileFil: Bogdanovich, José M.. Pontificia Universidad Católica de Chile; ChileFil: Bozinovic, Francisco. Pontificia Universidad Católica de Chile; Chil

¿La presencia de ganado domesticado altera la conducta trófica de poblaciones simpátricas de los camélidos silvestres Vicugna vicugna Molina 1782 y Lama guanicoe Müller 1976 (Artiodactyla: Camelidae)? Evidencia de los Andes Centrales

We described and compared the diets of two sympatric Andean camelids, during the humid season (austral summer) in a site of Northern Chile, in presence of domestic livestock. Results indicate that: 1) grasses and shrubs are the main component in the diet of both camelids, 2) shrubs were more consumed by V. vicugna; 3) V. vicugna and L. guanicoe used the same trophic resources but in different proportions; 4) in mountain environments, wetlands exploitation by wild camelids seems restricted by domestic cattle, which would cause the displacement of Vicuñas and Guanacos to suboptimal habitat for feeding.Describimos y comparamos la dieta de dos poblaciones simpátricas de camélidos silvestres, durante la estación húmeda (verano) en un sector del norte de Chile en presencia de ganado domesticado. Nuestros resultados indican que: 1) gramíneas y arbustos son el principal componente de la dieta de ambos camélidos; 2) arbustos fueron consumidos principalmente por V. vicugna; 3) V. vicugna and L. guanicoe utilizan los mismos recursos tróficos pero en diferentes proporciones; 4) en ambientes de montaña, el uso de vegas altoandinas por parte de camélidos silvestres estaría siendo restringido por la presencia de ganado domesticado, el cual provocaría el desplazamiento de ambos camélidos a zonas subóptimas de alimentación