Phenotypic plasticity in the timing of reproduction in Andean bears

Abstract

Many factors influence whether mammals reproduce seasonally or continuously but disentangling them can be challenging in free‐living species that are hard to observe. We described the seasonality of reproduction in Andean bears (Tremarctos ornatus) in NW Peru (6°26′S, 79°33′W) to test for phenotypic plasticity in response to extrinsic cues. To do so, we compared the mating behavior and birthdates of free‐living bears to the birthdates of captive bears housed over a broad range of latitudes. Free‐living bears were observed on 302 occasions over 6 years (967 field‐days), and mating behaviors recorded 61 times from late Dec to Jan. The mean birthdate of 12 wild‐born litters was 17 August (range = 23 Jun – 15 Oct), 57 ± 10 (SD) days after the winter solstice. Birthdates for 367 captive litters varied widely by comparison (range = 1 Jan – 31 Dec; mean = 14 ± 49 days after the winter solstice). However, captive bears in the tropics had fewer births in autumn and winter (71.4% of births) than captive bears at higher latitudes (96.8% of births; P < 0.001). Differences in seasonal reproduction among captive bears at high and low latitudes and captive and a free‐living at tropical latitudes suggest that Andean bears display phenotypic plasticity in reproductive timing but influenced by photoperiod at high latitudes. Because photoperiodic effects were less evident at tropic latitudes, we suggest that seasonality in the timing of reproduction in the free‐living bears we observed was influenced by seasonal variation in food abundance. The observed effect of photoperiod on reproduction in captive Andean bears at high latitudes may also imply that free‐living bears at the southern edge of the range may be constrained in their ability to adjust reproductive timing to resource availability as environments change.

Phenology of brown bear breeding season and related geographical cues

“…Bear species inhabiting areas near the equator (e.g. sloth bear Melursus ursinus, Shaw 1971, and spectacled bear Tremarctos ornatus, Cuvier 1825) may copulate throughout the year in the wild, but show a seasonal pattern when kept in captivity at higher latitudes (Spady et al 2007;Appleton et al 2018), which supports the relevant role of the photoperiod in breeding season phenology in ursids. However, we did not find a similar day length across study areas at the start of the breeding season, as expected, but instead a longer day length in northern areas.…”

The Andean bear alopecia syndrome may be caused by social housing

“…We therefore hypothesize that the alopecia syndrome in Andean bears may be only the most obvious symptom of endocrine abnormalities or autoimmune responses caused by the long‐term social housing of bears that would not otherwise live in groups. As best as we know, adult Andean bears socialize only for mating (Appleton et al, ). Other bears are also solitary, but they nevertheless may congregate for short periods of time at natural or artificial food sources or other resources.…”

“…For diverse reasons, adult bears are sometimes housed socially. However, adult wild bears, including Andean bears (Appleton et al, ), are thought to directly interact primarily for reproductive purposes, except for brief periods of social interaction when localized resources are abundant (American black bears, Ursus americanus : Herrero, ; Rogers, ; brown bears, Ursus arctos : Clapham & Kitchin, ; Gill & Helfield, ; Peirce & Van Daele, ; Penteriani et al, ; and polar bears, Ursus maritimus : Herreman & Peacock, ). Thus, social stress experienced by a typically non‐social bear species has been suggested as one possible risk factor for the Andean bear alopecia syndrome (Drake, Bechstein, & Kolter, ; Jäger et al, ).…”

First confirmed record of Jaguarundi, Herpailurus yagouaroundi (&Eacute;. Geoffroy, 1803) (Mammalia, Carnivora, Felidae), on the western slope of the Peruvian Andes

“…Each station included two camera traps (one Reconyx and one Bushnell Trophy Cam) facing each other at two sides of a game trail or waterholes. The cameras were set at approximately 40 cm above the ground, with no bait, and were set to take five photos (on Reconyx) and three photos (on Bushnell Trophy Cam) per trigger with a one second interval during 24 hours per day (Appleton et al 2018).…”