Seasonal or photoperiodically sensitive animals respond to altered day length with changes in physiology (growth, food intake and reproductive status) and behaviour to adapt to predictable yearly changes in the climate. Typically, different species of hamsters, voles and sheep are the most studied animal models of photoperiodism. Although laboratory rats are generally considered nonphotoperiodic, one rat strain, the inbred Fischer 344 (F344) rat, has been shown to be sensitive to the length of daylight exposure by changing its physiological phenotype and reproductive status according to the season. The present study aimed to better understand the nature of the photoperiodic response in the F344 rat. We examined the effects of five different photoperiods on the physiological and neuroendocrine responses. Young male F344 rats were held under light schedules ranging from 8 h of light/day to 16 h of light/day, and then body weight, including fat and lean mass, food intake, testes weights and hypothalamic gene expression were compared. We found that rats held under photoperiods of ≥ 12 h of light/day showed increased growth and food intake relative to rats held under photoperiods of ≤ 10 h of light/day. Magnetic resonance imaging analysis confirmed that these changes were mainly the result of a change in lean body mass. The same pattern was evident for reproductive status, with higher paired testes weight in photoperiods of ≥ 12 h of light/day. Accompanying the changes in physiological status were major changes in hypothalamic thyroid hormone (Dio2 and Dio3), retinoic acid (Crabp1 and Stra6) and Wnt/β-Catenin signalling genes (sFrp2 and Mfrp). Our data demonstrate that a photoperiod schedule of 12 h of light/day is interpreted as a stimulatory photoperiod by the neuroendocrine system of young male F344 rats.

Graphical abstract

Farmers in developing countries often work in challenging environments with poor infrastructure, marginal agricultural potential, and limited economic opportunities. These challenges are exacerbated when wildlife impact human livelihoods. Here, we analyze data quantifying the type and frequency of human‐wildlife impacts within communal conservancies across Namibia and explore possible drivers of temporal and spatial variation of these data. A total of 112,165 human‐wildlife impacts were reported between 2001 and 2019 at the national level, with livestock depredation the most common. Marked regional variation was however evident with crop raiding and attacks on humans more prevalent in the mesic North‐East, and both livestock depredation and infrastructure damage highest in the arid north‐western regions. Elephant, jackal, hyena, cheetah, and leopard (in descending order) were the species most frequently linked to reported damage. Distance to the nearest protected area and river, terrain ruggedness, conservancy size, and annual rainfall (amongst others) all had a significant impact on both the distribution and extent of human‐wildlife impact reports. Reports did not vary significantly with years but were significantly influenced by average monthly rainfall. Understanding spatial and temporal patterns of human‐wildlife impacts at a national scale, in addition to their potential drivers, allows for the identification of conflict hotspots and the allocation of resources and expertise to mitigate them. Ultimately, mitigating negative interactions between people and wildlife will allow for the continued sharing of space and with that the sustainability of a model that has seen a dramatic increase in both the distribution and abundance of wildlife in Namibia.