The frequency of antlerless females among Svalbard reindeer

The distribution of females with no, one and two antlers was recorded during July 1994 in Svalbard reindeer, Rangifer tarandus platyrhynchus, and compared wirh 1974 data from Reimers (1993) and Larsen (1977). On Reinsdyrflya, 50% of the females were anrlerless, 16% one antlered and 34% rwo antlered. In Nordenskiold Land, 2% of rhe females were antlerless, 1% one antlered and 97% two antlered. These percentages have not changed since Reimers' study in 1974 in Reinsdyrflya (%2 = 1.16, P > 0.05) and Nordenskiold Land (%2 = 1.69, P > 0.05). The reason for the high frequency of anrlerless females on Reinsdyrflya is not understood.


Introduction
Reindeer and caribou (Rangifer tarandus) are the only species in the cervid family where both sexes develop antlers.However, antlerless females have been observed in various sub-species, areas and populations, and some populations have been observed to have significant variations over time with regards to antler frequency (see review by Reimers, 1993).Although Rangifer male antler cycle is under endocrine control (Lincoln & Tyler, 1992;Lincoln & Tyler, 1994), both antler size and the shedding pattern are influenced by nutrition (Wika, 1980;Lincoln & Tyler, 1994).However, the control of the Rangifer female antler cycle is not clear.
This paper accesses the relative numbers of female Svalbard reindeer (R. t. platyrhyncus) with and without antlers from two regions of Svalbard.

Rangifer, 18 (2): 81-84
Observations of antler status were made for Reinsdyrflya and Nordenskiold Land (Fig. 1) during July 1994, when the growing antler are in velvet.These observations were compared to observations from earlier studies from the same two regions including 1988 from Severinsen (pers. comm., unpubl.).For the purposes of discussion, Larsen's (1977) and Severinsen's (pers. comm., unpubl.)observations on antler status from a third region, Nordaustlandet (Fig. 1), are considered.Possible determinants of female antler status are discussed.
Reindeer were categorized according to sex and age (calves and 1 yr+), and the presence/absence of antlers was recorded through direct observations of free ranging individuals.Sex was determined by watching reindeer while they urinated.Chi-square analysis was used to examine the difference in frequency of antler distribution in Nordenskiold Land and Reinsdyrflya within and between years.Fisher's exact test was performed to adjust for having only one degree of freedom.However, the P-value was so similar to the Pearson's P-value thar the latter was chosen.The expected values were rounded off to the nearest whole number.JMP™ statistical package version 3.02 was used for statistical calculations.

Results and discussion
We found no significant change between the three antler categories on Reinsdyrflya from earlier studies starting in 1974 (Reimers, 1993) to our own 1994 study (Table 2 and 3).Unpublished data from 1988 (Severinsen, pers.comm.)supports this observation.In August 1988, 49% of the females on Reinsdyrflya were antlerless (Severinsen, pers. comm., unpubl. data).In 1994, the presence of antlerless females in Nordenski0ld Land was minute (2%), and no significant change has occurred in the distribution of the three antler categories since Reimers's 1974 study (Reimers, 1993) (Table 2 and  3).On Nordaustlandet, all females observed in 1974 (Larsen, 1977) and1994 (Severinsen, pers. comm., unpubl. data) were antlered (Table 3).The data from the present and other studies indicate a stable frequency in the antler distribution among female reindeer in the three regions.This suggests a persistent factor, or set of factors, present to maintain the high level of antlerless and one antlered females on Reinsdyrflya, and likewise, two antlered females in the other two regions.
Among the several possible hypotheses for what may determine antler development, we have considered two; nutrition and genetics: HI: Plant biomass will determine antler status.We looked at the literature on summer pastures for a comparison of Land from Tyler and Hindrum (pers.comm.).Data from Nordaustlandet on area size from Staaland & Punsvik (1980).
Population size and range quality in Nordaustlandet from Hindrum et al. (1995).Own observations from Reinsdyrflya.Svalbard, 1974Svalbard, , 1988Svalbard, and 1994. .H2: Genetic differences in sub-populations determine antler status.It has been suggested that reindeer from different populations on Svalbard (Reinsdyrflya, Edgeøya/Barentsøya and Nordaustlandet) have separate gene pools (Staaland & Røed, 1985).The population of reindeer on Svalbard was hunted to near extinction by 1925.It is possible that a population «bottle-neck» at that time caused a genetic drift in the population on Reinsdyrflya.Reinsdyrflya is inhabited by a relatively isolated population, and the trait of antlerless females could have developed due to genetic drift.
It is also conceivable that a variable selection pressure leads to the observed antler status in the different regions.; Information from Severinsen (pers.comm).
the three regions.Nordenskiold Land represents an area with dense biomass cover (Punsvik et al., 1980).During summer months, the valleys in this area offer a rich variety of herbs, grasses, mosses and bushes.Reinsdyrflya represents an area with medium biomass cover, dominated by mosses and grasses (Saevre, 1982).Nordaustlandet is clearly the area with lowest biomass cover, with a few herbs and monocotyledons available for pasture (Staaland & Punsvik, 1980).Reindeer exposed to the lowest plant biomass, Nordaustlandet, all carried two antlers.It appears that plant biomass gradient does not determine antler status.However, the possibility remains that other differences in range properties exist among the three regions that are involved in their respective differences in female reindeer antler status.

Table 1 .
Characteristics of Nordenskiold Land Adventdalen (AD), Colesdalen (CD), Semmel/Reindalen (S/RD), and Sassendalen (SD), Reinsdyrflya and Nordaustlandet.Area corresponding to the vegetation cover below 250 m a.s.l. for Nordenskiold Land and Reinsdyrflya and area not covered by ice on Nordaustlandet.' Density (abundance) of reindeer in relation to suitable habitat.Data on area and number of reindeer on Nordenskiold

Table 3 .
The frequency of female reindeer wirh two, one and no antlers on Nordenskiold Land, Reinsdyrflya and Nordaustlandet,