Geographic and seasonal variability in feeding behaviour of a small herbivorous rodent

Gastrointestinal morphology is an effective functional dietary proxy that predicts small mammal community structure

The availability and quality of food resources can alter the intensity of competition and predation pressure within communities. Understanding species capacity to respond to global change-driven shifts in resource distribution is therefore crucial for biodiversity conservation. Small mammal communities are often structured by competition for food resources, but understanding and monitoring these processes are currently hindered by lack of functional dietary trait information in these hard-to-sample systems. In this study, we collected a comprehensive suite of gastrointestinal (GI) measurements from 26 small mammal species (including some never reported), compared them with more traditional craniodental traits in predicting dietary guild, and used them in a novel way to understand how diet structures 22 small mammal communities across the Appalachian Mountains of eastern North America. As predicted, we found GI traits to be effective dietary trait proxies; they were equally or more accurate than craniodental proportions in predicting the dietary guild of individual species. Furthermore, at the community level, we found that both the mean and functional dispersion of GI length were positively correlated with latitude and measures of temperature seasonality. Our results indicate that small mammal communities in more seasonal environments are filtered to include species with longer GI tracts (on average) as well as those that can partition food resources more finely, as expected based on the lower productivity of these regions. Conversely, communities in less seasonal environments display functional redundancy from the addition of species with short to intermediate GI lengths. Proportions of the GI tract represent novel dietary traits that can illuminate community assembly processes across regional environmental gradients and in the face of changing timing and availability of resources.

Feeding ecology of Massoutiera mzabi (Rodentia, Ctenodactylidae) in two national parks of Central Sahara

The present range of Massoutiera mzabi is restricted to deserts and semi-deserts of the northern and Central Sahara, and discontinuously to Aïr Massif and Adrar of Ifoghas. Vegetation seems to be the second main driver of occurrence of this herbivorous rodent, so we investigated its diet selection by comparing the contents of faeces collected from two stations of the national parks of Ahaggar (Chaabet Tidekatine) and Tassili n’Ajjers (Oued Izarwaz) to the availability of plants nearby. The diet included a total of 25 plant species, 14 from Chaabet Tidekatine and 20 from Oued Izarwaz. In Chaabet Tidekatine, Zygophyllaceae (mainly Fagonia glutinosa and Fagonia bruguieri) over Asteraceae (Pulicaria incisa) and Poaceae (Stipagrostis). In Oued Izarwaz, the most consumed plant species were Asteraceae (Pulicaria crispa and P. incisa), Poaceae (Stipagrostis pungens) and Capparidaceae (Cleome amblyocarpa). Overall, M. mzabi diet appeared to be influenced more by the diversity than by the availability of vegetation. Seasonal variations in diet indicate that this rodent eats perennial and ambivalent vegetation throughout the year and opportunistically consumes annual plants mainly in the spring, with the exception of P. incisa and P. crispa which were eaten throughout the year.

First quantitative data on the feeding ecology of an arid zone rodent, the Common gundi (Ctenodactylus gundi)

One species of the family Ctenodactylidae, the Common gundi, Ctenodactylus gundi, occupies a restricted area between the Saharan and Mediterranean domains where annual rainfall is between 50 and 400 mm. Its presence seems also conditioned by the vegetation, so its feeding ecology was investigated by the microhistological analysis of faeces collected in two stations (Baniane and Bazem) of the Aurès massif (Eastern Algeria) during two years from June 2015 to May 2017, and by the evaluation of the available food. The diet included a total of 34 plant species, 16 in Baniane and 20 in Bazem. Results show that in Baniane, Asteraceae were predominant with Artemisia herba-alba (relative abundance, A% = 33.13%), followed by Fabaceae with Argyrolobium uniflorum (A% = 20.32%) and Poaceae with Aristida sp. (A% = 14.95%). In Bazem, the most consumed plant species were Lamiaceae with Thymus ciliatus (A% = 42.77%) and Poaceae with Lolium rigidum (A% = 13.19%). Overall, C. gundi fed on a large number of plant species, and its diet appeared to be influenced more by the diversity than by the availability of vegetation. Seasonal variations in diet indicate that this rodent eats perennial vegetation throughout the year and opportunistically consumes annual plants to a lesser extent in the spring, with a certain time shifting between the two stations probably due to rainfall and temperature differences.

Costs of exploratory behavior: the energy trade-off hypothesis and the allocation model tested under caloric restriction

In order to maintain the energy balance, animals often exhibit several physiological adjustments when subjected to a decrease in resource availability. Specifically, some rodents show increases in behavioral activity in response to food restriction; a response regarded as a paradox because it would imply an investment in locomotor activity, despite the lack of trophic resources. Here, we aim to explore the possible existence of trade-offs between metabolic variables and behavioral responses when rodents are faced to stochastic deprivation of food and caloric restriction. Adult BALB/c mice were acclimatized for four weeks to four food treatments: two caloric regimens (ad libitum and 60% restriction) and two periodicities (continuous and stochastic). In these mice, we analyzed: exploratory behavior and home-cage behavior, basal metabolic rate, citrate synthase and cytochrome oxidase c enzyme activity (in liver and skeletal muscle), body temperature and non-shivering thermogenesis. Our results support the model of allocation, which indicates commitments between metabolic rates and exploratory behavior, in a caloric restricted environment. Specifically, we identify the role of thermogenesis as a pivotal budget item, modulating the reallocation of energy between behavior and basal metabolic rate. We conclude that brown adipose tissue and liver play a key role in the development of paradoxical responses when facing decreased dietary availability.

Renal intraspecific variation along an aridity gradient detected by new renal indices in a desert herbivorous rodent

Mammals that live in arid and semi-arid environments in South America present physiological mechanisms that enable them to conserve water. Body water is lost through the kidneys, lungs, skin, and intestines. Regarding renal adaptation for water conservation, several indices have been used to estimate the capacity of the kidneys to produce a maximum urine concentration. Most studies were conducted at an inter-specific level, with only few performed at the intraspecific level. In this work, we compare renal function and morphology among five populations of Southern mountain cavy, Microcavia australis, present along an aridity gradient. We hypothesized that individuals from drier zones would present morphological and functional renal modifications that imply a greater capability to conserve body water. These features were studied considering the classical indices (RMT, PMT, PMA, and RMA) and three new indices that consider area measurements; the latter showed to be more adequate to reflect intraspecific differences. Our results suggest that the morphological modifications of kidneys, that is, the greater areas of renal inner medulla, would be related to the aridity gradient where populations of Southern mountain cavy occur.