Seasonal coat color distribution of Mustela frenata (Long-tailed Weasel)

in North America

What influences the color of long tail weasel individuals found in an area of transition?

The long tailed weasel is a very successful small carnivores. In North America they exploit habitats ranging from prairies to forests to arctic tundra and are geographically distributed throughout the conintental U.S.

Kelly MathesonWinter Ecology – Spring 2006

Mountain Research Station – University of Colorado, Boulder

Seasonal coat color distribution of Mustela frenata (Long-tailed Weasel)

in North America1. Seasonal coat color change

2. Physiology of seasonal molt

3. Advantages of seasonal molt

4. Distribution of Mustela frenata

5. Factors influencing the molt

Seasonal coat color change

• All three species of N. Amercian weasels and other species of mammals from arctic foxes, hares and lemmings, molt to a white coat in the winter and brown coat in the summer

Seasonal coat color change

• In species that do change and have been studied, the change from one color to another is the result of a molt, the loss of fur, of one color, and the growth of fur of a different color.

Fig. 1 Overview of physiology of molt and color change in weasels.Feder, S. 1990

Why molt to white?

• White coat offers a thermal advantage -

•Feist & White suggest that a white coat may be better suited in cold, sunny and windy conditions at wind speeds in excess of 3 m/s, thereby allowing more incident UV radiation to the skin. •But, insulative qualities of fur are dependent on length and density of fur.

•According to King (1989), pelage depth and density do not significantly change in weasels. •And, smaller mammals like weasels have a larger surface area to volume ratio, demonstrating an increased mass specific rate of heat loss.

Why molt to white?

• White coat offers a thermal advantage -

•Length of fur and fat accumulation are limited by hunting behavior of weasels.

•This coupled with the long thin shape of the weasel does not appear to support the theory that a seasonal molt to white offers any thermal advantage to the long tailed weasel.

Why molt to white?

• White coat offers a thermal advantage - Not likely

•White coat serves the purpose of camouflage •Weasels do not practice the sit and wait strategy of hunting.•Solitary searchers, specializing in the ability to explore every nook and cranny for small prey, cannot camouflage movement.

Why molt to white?

• White coat offers a thermal advantage - Not likely

•White coat serves the purpose of camouflage

A white winter coat is not an adaptation to cold but rather for camouflage, both to avoid predators and to aid in the pursuit of prey.

Fig. 2 Limit of winter whitening in long tailed weasels (Mustela frenata).(map redrawn from Hall 1951)

Suggested influences of north/south distribution

• Temperature - populations differ in response to temperature (King 1989)– Pop. Living in climatic extremes do not need

flexibility of those found in area of transition. A temp. switch is what determines color of molt.

– Studies by Rothschild(1942), Feder (1990)…etc demonstrated coat color is directly related to area of origin for individuals.

– Unlikely that mechanism determining color change would be present at the individual level rather then population as a whole.

Suggested influences of north/south distribution

• Assuming an individual changes color to escape detection, then it makes sense that the transition zone is maintained by natural selection.

• The disadvantage of remaining brown must be severe because all Arctic weasels turn white in

the winter

Suggested influences of north/south distribution

• Hewson & Watson (1979) looked at the relationship between winter whitening, snow cover, and temperature in Scotland and

Yorkshire • Found that differences in proportion turning

white between different regions and altitudes within regions were positively associated with number of days of snowfall and snow lie and inversely with monthly minimum temperature.

What we do know?

• The fall molt is initiated by photoperiod.• Individual fall molt color change appears to be genetically

determined.• Days of snow lie, not temperature, influence proportion of white

individuals found.• The color of hair growth following molt appears to be

determined by the presence or absence of MSH - acts as an intracellular blocking factor

Where are we going?

• Would transition zone outlined by Hall (1951) be located in same areas today?

• DNA and breeding experiments over several generations.

• May provide an opportunity to study natural selection in short time frame.

• Is new white growth the result of the prolactin inhibition or the high levels of melatonin that cause inhibition of MSH?

•Bissonnette, T. and E. Wilson. 1939. Shortening daylight periods between May 15 and September 12 and the pelt cycle of the mink. Science. 89:418.•Feder, S. 1990. Environmental determinants of seasonal coat color change in weasels (Mustela erminea) from two populations. M.S. Thesis. University of Alaska Fairbanks. •Feist, D. and R. White. 1989. Terrestrial mammals in cold. In advances in Comparative and Environmental Physiology, vol. 4, edited by L. Wang, Springer-Verlag Berlin Heidelberg. •Hall, E.R. 1951. American Weasels. University of Kansas Museum of Natural History. 4:1-466.•Hewson, R. and A. Watson. 1979. Winter whitening of stoats (Mustela erminea) in Scotland and Northeast England. Journal of Zoology. 187:55-64

References

•King, C.M. 1989. The Natural History of Weasels and Stoats. Comstock Publishing Association., Cornell University Press, N.Y. •Rust, C.C. 1965. Hormonal control of pelage cycles in the short tailed weasel (Mustela erminea bangsi). General and Comparative Endocrinology. 5:222-231.

References