Reproduction of plateau pika (Ochotona curzoniae) on the Qinghai–Tibetan plateau

The effects of grassland degradation on the genetic structure of a small mammal

Grassland degradation is challenging the health of grassland ecosystems globally and causing biodiversity decline. Previous studies have demonstrated the impact of grassland degradation on the abundance and behavior of small mammals. Little is known about how it affects the genetic structure of gregarious mammals in the wild. This study explores the effects of grassland degradation on the genetic structure of a small burrowing mammal, plateau pika (Ochotona curzoniae). We used nine microsatellite loci to analyze the genetic diversity and genetic differentiation between colonies and genetic relatedness between individuals within the colony. We found that pikas in severely degraded grasslands had a significantly higher genetic diversity within colonies, a higher level of gene flow between colonies, and a lower genetic differentiation between colonies compared to pikas in less degraded grasslands. Individuals within colonies had a significantly lower genetic relatedness in severely degraded grasslands than in less degraded grasslands. This study has provided potential evidence of a significant impact of grassland degradation on the genetic structure of pikas, which has caused a breakdown of their kin-selected colony structure.

Phylogeography of the Plateau Pika (Ochotona curzoniae) in Response to the Uplift of the Qinghai-Tibet Plateau

The evolution and current distribution of species on the Qinghai-Tibet Plateau have been significantly impacted by historical occurrences, including the uplift of the plateau and the Quaternary climate upheaval. As a remnant species, the plateau pika (Ochotona curzoniae) is a great model for researching historical events. In this study, 302 samples from 42 sample sites were utilized to analyze the impact of historical events on the evolution and distribution pattern of plateau pikas. The genetic diversity, patterns of differentiation, and historical dynamics of the plateau pika were investigated using molecular markers that included four mitochondrial genes (COI, D-loop, Cytb, and 12S rRNA) and three nuclear genes (GHR, IRBP, and RAG1). The results showed that: (1) The genetic diversity of the plateau pika was high in the Tibetan Plateau (Hd = 0.9997, π = 0.01205), and the plateau pika evolved into five lineages that occupied different geographical areas, with lineage 1 (Group 1) in the south of the Yarlung Zangbo River, lineage 2 (Group 2) in the hinterland of the plateau, lineage 3 (Group 3) in the northeastern part of the plateau, lineage 4 (Group 4) in the Hengduan Mountains, and lineage 5 (Group 5) in the eastern part of the plateau. (2) The gene flow among the five lineages was low, and the differentiation level was high (Nm < 0.25; Fst > 0.25), indicating that the geographical barriers between the five lineages, such as the Yarlung Zangbo River, the Qaidam-Ghuong-Guide Basin, and the Lancang River, effectively promoted the population differentiation of the plateau pika. (3) The plateau pika first spread from the Hengduan Mountains to the entire Qinghai-Tibet Plateau and then conducted small-scale migration and dispersal in several refuges across the plateau in response to climate changes during the glacial and interglacial periods. (4) Except for Group 1 and Group 4, all the other populations exhibited a rapid expansion between 0.06 and 0.01 Mya, but the expansion was considerably delayed or halted by the effects of climate change during the last glacial maximum (0.02 Mya). Overall, the plateau pika on the Qinghai-Tibet Plateau exhibits high genetic diversity, and topographic obstacles, including mountains, valleys, and basins, created by the uplift of the plateau and climatic changes since the Quaternary period have played an important role in the differentiation and historical dynamics of the plateau pika population.

Seasonal variations in the composition and functional profiles of gut microbiota reflect dietary changes in plateau pikas

Seasonal variations in gut microbiota of small mammals and how it is influenced by environmental variables is relatively poorly understood. We sampled 162 wild plateau pikas (Ochotona curzoniae) in four seasons over two and a half years and recorded the air temperature, precipitation, and nutrient content in edible vegetation at the sampling site. After conducting 16S rRNA and shotgun metagenomic sequencing, we found that the highest alpha diversity, the relative abundance of Firmicutes, and the simplest co-occurrence network occurred in winter, whereas that the highest relative abundance of Proteobacteria and the most complex network structure was observed in spring. The highest relative abundance of Verrucomicrobiota and Spirochaetota were seen in summer and autumn, respectively. Air temperature, precipitation, and the contents of crude protein, crude fiber, and polysaccharide in vegetation had significant effects on the seasonal changes in gut microbiota. Diet contributed more to microbial variation than climatic factors. Metagenomic analysis revealed that the amino acid metabolism pathway and axillary activity enzymes were most abundant in summer, while abundance of carbohydrate-binding modules and carbohydrate esterases were highest in spring. These microbial variations were related to the changes in dietary nutrition, indicating that gut microbiota of plateau pika contribute to the efficient use of food resources. This study provides new evidence of how external environmental factors affect the intestinal environment of small mammals. This article is protected by copyright. All rights reserved.

Maternal effects on reproduction in the precocial European hare (Lepus europaeus)

In female mammals, reproduction, and in particular lactation, is the energetically most exigent life-history phase. Reproduction is strongly controlled by body reserves and food availability, so females with better body condition or food supply are believed to have higher reproductive output. Additionally, the growth and mortality of young mammals depends on their postnatal development. Therefore, the degree of precociality affects energetic demands for both mothers and young. To study the reproductive performance of the precocial European hare (Lepus europaeus), we analysed relationships between six predictor variables describing maternal and environmental effects and nine response variables relating to reproduction from 217 captive females. We compared the data with those of precocial and altricial mammal species from an extensive literature search. For hares, we found: (1) Heavier females had heavier litters at birth. (2) In summer and spring, total litter mass was larger than in winter. (3) At the end of lactation, the litters of multiparous females were heavier than those of primiparous females. (4) Both older females and females giving birth for the first time had relatively high leveret mortality during lactation. Comparing our results with the literature for other mammals revealed that the body condition (i.e., body mass) of females before birth is predictive of reproductive parameters in both precocial and altricial species. In the precocial hare, female body condition is no longer predictive of reproductive parameters at the end of lactation, whereas in altricial species, female body condition remains predictive of reproduction (litter mass at the end of lactation, offspring mortality) until the end of lactation. We conclude that these effects are caused by precocial offspring feeding on solid food soon after birth and, thus, being less dependent on the mother's body condition during lactation than altricial offspring. In line with this, precociality might have evolved as a way of buffering offspring against maternal effects.

Among-population divergence in personality is linked to altitude in plateau pikas (Ochotona curzoniae

BACKGROUND

Animals inhabiting high altitudes consistently show slow life-histories. The pace-of-life syndrome (POLS) hypothesis posits behavioural, physiological and/or morphological traits that mediate the trade-off between current and future reproduction or survival, which have coevolved along a slow-fast life history continuum. Previous studies have shown that the life histories of plateau pikas varied across altitude, high-altitude individuals showed slow pace of life which were characterized by few litters per year with small litter sizes. Thus, we hypothesized that pikas populations at higher altitudes would also express personalities characteristic associated with slow life history, such as high sociability, low activity or aggressiveness. We tested this hypothesis by comparing the activity and docility of three plateau pika (Ochotona curzoniae) populations distributed along an altitudinal gradient of the Tibetan Plateau. We predicted that high-altitude pika would be more docile and less active.

RESULTS

The behaviour of 556 pikas, from which 120 individuals were measured at least twice, was quantified. We observed that plateau pikas at high altitudes were less active and more docile than pika at lower altitudes. Activity and docility were significantly and negatively correlated in populations from high altitudes but not in populations from low altitudes.

CONCLUSIONS

Our results support the POLS hypothesis, highlight the existence of personality variation among populations distributed along an altitudinal gradient and emphasise the importance of environmental selection on personality divergence.

Microhabitat use by plateau pikas: living on the edge

Mammals rely on habitat resources for survival and reproduction. We studied microhabitats used by plateau pikas (Ochotona curzoniae) of the Qinghai-Tibetan Plateau. Microhabitat features used by pikas include sedge meadows that provide forage, burrows that provide safety from predators and cover for nests, degraded open-dirt patches, and edges between sedge meadow and open dirt patches that often have a “lip” between those microhabitats. We investigated the extent to which these edges might serve as a preferred pika microhabitat. GIS techniques were used to overlay individual pika home ranges, determined by focal and scan sampling, on a digitized map containing microhabitat features. Regions that contained multiple coinciding individual home ranges, referred to as overlap polygons, were categorized numerically based on the number of individual home ranges that overlapped each polygon. These overlap polygons were used as relative measures of pika activity. We tested the spatial relationship between pika activity and the microhabitat features of edges, burrows, and proportional area of sedge. There was a significant relationship between the number of pikas in an overlap polygon and the number of pikas in an adjacent polygon. This pattern was controlled statistically to test whether activity was influenced by the presence of potentially favorable microhabitat features. Most of the variation in number of pikas that overlapped a habitat polygon was associated with the relative amount of “edge microhabitat” between sedge meadow and degraded open dirt patches (Cohen’s effect size, f2 = 0.91). Neither burrow openings nor sedge had a strong influence on the number of pika home ranges that overlapped. The importance of microhabitat edges appeared high for plateau pikas.

Response of leaf traits of common plants in alpine meadow to plateau pika disturbance

Leaf traits have been proven to reflect the adaptation of individual plants to disturbance environments in a grassland ecosystem. A field survey was conducted to investigate the effects of the disturbance intensity of plateau pika on the leaf traits of a dominant (Kobresia pygmaea) and two common plants (Elymus nutans and Anemone rivularis var. flore-minore) in an alpine meadow. This study indicated that the plateau pika disturbance enables the individuals of three plants to exhibit respective plasticity because the three plants had different leaf indices (LI) as the disturbance intensity increased. K. pygmaea, E. nutans and A. rivularis var. flore-minore had high specific leaf area (SLA), leaf dry mass content (LDMC), and leaf nitrogen content (LNC) at relatively low, moderate, and high disturbance intensities of plateau pika, respectively. K. pygmaea, E. nutans and A. rivularis var. flore-minore suffered low nutrient stress at low, moderate and high disturbance intensities due to high N : P at corresponding disturbance intensities. These results indicated that K. pygmaea, E. nutans and A. rivularis var. flore-minore grew well at relatively low, moderate, and high disturbance intensity conditions, respectively, which contributed to the improvement of alpine meadows with a higher proportion of E. nutans at a moderate disturbance intensity or the deterioration of alpine meadows with a higher proportion of A. rivularis var. flore-minore at a high disturbance intensity. Our findings suggest that leaf traits are effective tools to explain how small burrowing herbivore disturbances often lead to the improvement or deterioration of alpine meadows under different disturbance intensities.

Pika Population Density Is Associated with the Composition and Diversity of Gut Microbiota

Host population density is positively associated with the strength of social interactions or the frequency of physical contacts, and thus potentially influences microbial transmission among individuals. However, the relationship between host density and gut microbiota remains unknown. Here, we characterized the gut microbiota of plateau pikas (Ochotona curzoniae) in wild experimental fields with different host population densities. The abundance of some gut microbes significantly correlated with host density, such as Ruminococcaceae, Lachnospiraceae, and Staphylococcaceae. Intriguingly, host density was positively correlated with alpha diversity (Shannon diversity and observed species) of gut microbial communities. The inter-individual gut microbiota within high-density groups were more similar to each other than those of low-density groups. Host density significantly explained the variations in the gut microbiota, even after controlling sex, weight, diet and geographical locations. Based on the PICRUSt metagenome prediction, positive correlations were observed between host density and the relative abundances of 12 gene functions involved in cellular processes, environmental information processing and metabolism. These results indicate the importance of host density as a factor in shaping gut microbial composition and diversity in plateau pikas, and may further help us understand the social transmission of gut microbiota.