Mediterranean Pine Vole, Microtus duodecimcostatus: A Paradigm of an Opportunistic Breeder

Most mammalian species of the temperate zones of the Earth reproduce seasonally, existing a non-breeding period in which the gonads of both sexes undergo functional regression. It is widely accepted that photoperiod is the principal environmental cue controlling these seasonal changes, although several exceptions have been described in other mammalian species in which breeding depends on cues such as food or water availability. We studied the circannual reproductive cycle in males of the Mediterranean pine vole, Microtus duodecimcostatus, in the Southeastern Iberian Peninsula. Morphological, hormonal, functional, molecular and transcriptomic analyses were performed. As reported for populations of other species from the same geographic area, male voles captured in wastelands underwent seasonal testis regression in summer whereas, surprisingly, those living either in close poplar plantations or in our animal house reproduced throughout the year, showing that it is the microenvironment of a particular vole subpopulation what determines its reproductive status and that these animals are pure opportunistic, photoperiod-independent breeders. In addition, we show that several molecular pathways, including MAPK, are deregulated and that the testicular “immune privilege” is lost in the inactive testes, providing novel mechanisms linking seasonal testosterone reduction and testis regression.

Micromamíferos del Pleistoceno Superior del yacimiento de PRERESA en el valle del Manzanares y su contribución a la reconstrucción paleoambiental de la cuenca de Madrid durante el Pleistoceno

PRERESA (Getafe, Madrid) es un yacimiento del primer tercio del Pleistoceno Superior, final del MIS 5, del que se han excavado 255 m2, y donde se han recuperado 754 piezas líticas y abundantes restos de micro- y macrovertebrados. En este trabajo se aborda el estudio de los micromamíferos identificados en el yacimiento: Erinaceomorpha: Erinaceus europaeus; Soricomorpha: Crocidura russula; Chiroptera: Rhinolophus ferrumequinum; Rodentia: Eliomys quercinus quercinus, Apodemus sp., Cricetulus (Allocricetus) bursae, Arvicola aff. sapidus, Microtus cabrerae, Microtus duodecimcostatus; Lagomorpha: Oryctolagus cuniculus. Esta asociación faunística, fundamentalmente por la presencia de Microtus cabrerae, es del Pleistoceno Superior. El estadio evolutivo de Microtus cabrerae y Arvicola aff. sapidus indican la antigüedad de esta asociación dentro de la primera parte de dicho periodo, lo que es acorde con la fecha de 84±5,6 ka BP obtenida por OSL. Todos los taxones que se registran en PRERESA viven actualmente en la zona en la que se ubica el yacimiento, excepto Cricetulus (Allocricetus) bursae que se extinguió en la Península Ibérica al final del Pleistoceno Superior. Las observaciones realizadas sobre el material indican que la acumulación de restos de micromamíferos en el yacimiento es debida, en su mayor parte, a la acción de predadores, muy posiblemente a egagrópilas de aves rapaces. La asociación de micromamíferos de PRERESA indica unas condiciones de clima templado con cierta humedad y un desarrollo de la vegetación con algunas zonas boscosas y fundamentalmente áreas abiertas pero con vegetación arbustiva, herbácea, praderas secas y húmedas, y ribereña. En una comparación de los micromamíferos del yacimiento de PRERESA con los de los yacimientos del Pleistoceno Medio de Áridos 1 y Valdocarros, los datos indican que en los tramos bajos de los ríos Manzanares y Jarama hubo unas condiciones climáticas y paisajísticas similares en los momentos que representan estos yacimientos (Pleistoceno Medio avanzado y primer tercio del Pleistoceno Superior). Sin embargo, y al igual que sucede en la actualidad, estas condiciones fueron algo diferentes en el valle del Lozoya en la Sierra de Guadarrama durante el primer tercio del Pleistoceno Superior, según indica la asociación de micromamíferos de la Cueva del Camino (Pinilla del Valle, Madrid), que sugiere un clima relativamente más húmedo y un medio con una mayor variedad de biotopos. La asociación de micromamíferos del Pleistoceno Superior de PRERESA, en el tramo bajo del Manzanares, comparada con la de la Cueva del Camino que tiene una cronología similar, y con otras del Norte de Madrid del Pleistoceno Superior, pone de manifiesto según nuestras observaciones una diferenciación biogeográfica y paleoclimática ya durante este periodo entre unas y otras, de las que la zona limitante serían más o menos las estribaciones meridionales y centro-orientales del Sistema Central.

Factors influencing large-scale distribution of two sister species of pine voles (Microtus lusitanicus and Microtus duodecimcostatus): the importance of spatial autocorrelation

The Lusitanian pine vole ( Microtus lusitanicus (Gerbe, 1879)) and the Mediterranean pine vole ( Microtus duodecimcostatus de Selys-Longchamps, 1839) are sister species with burrowing habits and a restricted European distribution. Our aim was to assess the relative effect of environmental, soil, and spatial characteristics on the distribution of these species in Portugal, and obtain predicted occurrence maps for each species, particularly to identify areas of sympatry. We used spatial eigenvector mapping (SEVM) to describe the spatial autocorrelation in species data, and we partitioned the variance in species distributions to quantify the relative effects of environmental, soil, and spatial characteristics. The spatial variables explained the major part of variability in both species distributions and were more important than environmental or soil variables. The Lusitanian pine vole occurs in areas outside landscape units of grassland, higher rainfall, frost, and cambisols, with mostly acid soils, lower abundance of litosols, and presence of solonshaks. The Mediterranean pine vole is distributed in grassland areas within intermediate values of soil pH, dominated by litosols and luvisols, and lower rainfall, frost, and cambisols. Our results showed disjunct sympatric areas of small size and a parapatry boundary for the centre of Portugal, suggesting that contact zones are probably narrow.

Assessment of habitat quality in the Mediterranean pine vole (Microtus duodecimcostatus) by the study of survival rates

Habitat quality should be usefully defined in a demographic perspective. Survival and fecundity rates are sufficient to allow population persistence in a high-quality habitat but not in a low-quality habitat. The Mediterranean pine vole (Microtus duodecimcostatus) occurs in apple orchards in southern France, but its populations in this habitat are often driven to extinction by chemical control. However, recolonization occurs promptly when control ceases. We tested the hypothesis that meadows surrounding the orchards are high-quality habitats (sources) for the Mediterranean pine vole. We livetrapped four populations, three in apple orchards and one in a meadow. Survival rates were estimated using probabilistic open-population models. Our analysis led us to conclude that meadows are low-quality habitats, particularly since no juveniles survived in this habitat during the main part of the study. Recolonization of chemically controlled patches is probably allowed by asynchronous control among orchards. We further discuss the usefulness of probabilistic open-population models for the investigation of variations in survival rates both within and between populations.