Ontogeny of audible squeaks in yellow steppe lemming Eolagurus luteus: trend towards shorter and low-frequency calls is reminiscent of those in ultrasonic vocalization

Background Rodents are thought to be produced their human-audible calls (AUDs, below 20 kHz) with phonation mechanism based on vibration of the vocal folds, whereas their ultrasonic vocalizations (USVs, over 20 kHz) are produced with aerodynamic whistle mechanism. Despite of different production mechanisms, the acoustic parameters (duration and fundamental frequency) of AUDs and USVs change in the same direction along ontogeny in collared lemming Dicrostonyx groenlandicus and fat-tailed gerbil Pachyuromys duprasi. We hypothesize that this unidirectional trend of AUDs and USVs is a common rule in rodents and test whether the AUDs of yellow steppe lemmings Eolagurus luteus would display the same ontogenetic trajectory (towards shorter and low-frequency calls) as their USVs, studied previously in the same laboratory colony. Results We examined for acoustic variables 1200 audible squeaks emitted during 480-s isolation-and-handling procedure by 120 individual yellow steppe lemmings (at 12 age classes from neonates to breeding adults, 10 individuals per age class, up to 10 calls per individual, each individual tested once). We found that the ontogenetic pathway of the audible squeaks, towards shorter and lower frequency calls, was the same as the pathway of USVs revealed during 120-s isolation procedure in a previous study in the same laboratory population. Developmental milestone for the appearance of mature patterns of the squeaks (coinciding with eyes opening at 9–12 days of age), was the same as previously documented for USVs. Similar with ontogeny of USVs, the chevron-like squeaks were prevalent in neonates whereas the squeaks with upward contour were prevalent after the eyes opening. Conclusion This study confirms a hypothesis of common ontogenetic trajectory of call duration and fundamental frequency for AUDs and USVs within species in rodents. This ontogenetic trajectory is not uniform across species.

Long-term monitoring reveals topographical features and vegetation explain winter habitat use of an arctic rodent

The quality of wintering habitats, such as depth of snow cover, plays a key role in sustaining population dynamics of arctic lemmings. However, few studies so far investigated habitat use during the arctic winter. Here, we used a unique long-term time series to test whether lemmings are associated with topographical and vegetational habitat features for their wintering sites. We examined yearly numbers and distribution of 22,769 winter nests of the collared lemming Dicrostonyx groenlandicus (Traill, 1823) from an ongoing long-term research on Traill Island, Northeast Greenland, collected between 1989 and 2019, and correlated this information with data on dominant vegetation types, elevation and slope. We found that the number of lemming nests was highest in areas with a high proportion of Dryas heath, but was also correlated with other vegetation types, suggestingsome flexibility in resource use of wintering lemmings. Furthermore, lemmings showed a higher use for sloped terrain, probably as it enhances the formation of deep snow drifts which increases the insulative characteristics of the snowpack and protection from predators. With global warming, prime lemming winter habitats may become scarce through alteration of snow physical properties, potentially resulting in negative consequence for the whole community of terrestrial vertebrates.

Comparative 2D-shape analyses of collared lemmings in the zone of possible sympatry between Dicrostonyx groenlandicus and Dicrostonyx richardsoni (Rodentia, Arvicolinae)

Morphological differentiation and relationships among collared lemmings (Dicrostonyx Gloger, 1841) remain unclear. This issue is particularly important in the Kivalliq Region, Nunavut, Canada, where Dicrostonyx groenlandicus (Traill, 1823) and Dicrostonyx richardsoni Merriam, 1900 ranges overlap. Possible sympatry of both species obscures the taxonomic status of collared lemmings from this area. We compared 2D outline shapes of the skull and three upper molars of collared lemmings collected from seven areas of the Canadian Arctic, including specimens from the Baker Lake – Aberdeen Lake area, in the Kivalliq Region, and Dicrostonyx hudsonius (Pallas, 1778) as an outgroup. Multivariate analyses revealed two distinct groups when considering the molars: D. hudsonius, and the remainder of lemmings. Dicrostonyx richardsoni, D. groenlandicus, and the lemmings from the Baker Lake – Aberdeen Lake area showed significant differences, especially when considering skull shapes, thus suggesting three distinct groups. However, skull shapes proved inefficient in discriminating between species. These differences suggest that collared lemmings from the Baker Lake – Aberdeen Lake area may not be correctly assigned to either of the two species without further genetic evaluation. They also suggest that these lemmings should have a peculiar taxonomic status. Our study calls for further taxonomical investigations for collared lemmings from the overlapping distribution ranges of D. groenlandicus and D. richardsoni.

Differences in behavior help to explain lemming coexistence

Collared (Dicrostonyx groenlandicus) and brown (Lemmus trimucronatus) lemmings coexist in tundra habitats across much of the middle and lower Canadian arctic. Their coexistence, and response to predation risk, appears mediated by behavior. We analyzed field-collected videos of open-field tests to assess potential differences in innate behaviors between the two species. Collared lemmings were less active and exhibited less exploratory behavior than did brown lemmings, which were more active under cover than in the open. Similar behaviors scaling along axes of activity and curiosity were revealed by principal components analysis. Each axis defined different aspects of brown lemming personality, but repeated testing of the same individuals yielded a striking dependence of their behavioral response on open-field treatments. Even so, the differences between species in behavior correlate well with their habitat preferences that resolve competition and govern their coexistence.

Fluctuations in lemming populations in north Yukon, Canada, 2007–2010

We estimated population density of brown lemmings ( Lemmus sibiricus (Kerr, 1792)), Greenland collared lemmings ( Dicrostonyx groenlandicus (Traill, 1823)), and tundra voles ( Microtus oeconomus (Pallas, 1776)) on Herschel Island from 2007 to 2010 by mark–recapture on three live-trapping areas. Limited data were also available from Komakuk Beach on the north Yukon coast. In contrast to most previous studies, brown and collared lemmings were partly out of phase. Brown lemmings on Herschel reached peak density in 2007–2008 and were low in 2009–2010, while collared lemmings were at peak density in 2007–2008 and again in 2010. Large adult male body size was characteristic of peak populations. Brown lemmings increased dramatically in the peak summer of 2008 and collared lemmings increased rapidly when winter breeding under the snow was successful in 2009–2010. By contrast, at Komakuk Beach, we could see no clear signs of fluctuations in these three species. Winter snow conditions may be too severe for population persistence on the coastal plain along the north coast of the Yukon. Further work is needed to unravel why peak lemming densities are so variable among sites and why lemming fluctuations are so pronounced on the arctic coastal plain of Alaska and virtually absent on the coastal plain of the north Yukon.