Katherine Ralls

MAMMALS IN WHICH FEMALES ARE LARGER THAN MALES

Females are larger than males in more species of mammals than is generally supposed. A provisional list of the mammalian cases is provided. The phenomenon is not correlated with an unusually large degree of male parental investment, polyandry, greater aggressiveness in females than in males, greater development of weapons in females, female dominance, or matriarchy. The phenomenon may have evolved in a variety of ways, but it is rarely, if ever, the result of sexual selection acting upon the females sex. The most common selective pressures favoring large size in female mammals are probably those associated with the fact that a big mother is often a better mother and those resulting from more intense competition among females for some resource than among males. It appears that, in general, more than one such pressure must affect the females of a species, and that their combined effects must not be countered by even stronger selective pressures favoring large size in males, before the result is that of larger size in the female sex. Sexual selection may often be operating upon the male sex in mammals even when it is the smaller. Present knowledge about the species of mammals in which females are larger than males is quite rudimentary. Much more information is needed before we will be able to speak of the selective pressures accounting for the phenomenon with any reasonable degree of certainty. Perhaps the most fruitful approach would be a series of field studies of groups of related species in which females are larger in some species and males are larger in others.

Mammalian Scent Marking

Mammals mark frequently in any situation where they are both intolerant of and dominant to other members of the same species. In other words, they mark when they are likely to attack another member of the same species, and are likely to win if they do attack. Such a situation occurs, as Hediger (13) pointed out, in connection with territoriality but it also occurs in other kinds of social systems. Frequent, vigorous marking occurs at times when there is reason to infer that the animal is motivated to aggression. The effects of marks and marking upon other individuals are poorly understood. Many species mark with more than one source of scent in response to one stimulus or set of stimuli.

SEXUAL DIMORPHISM IN MAMMALS: AVIAN MODELS AND UNANSWERED QUESTIONS

Current models for the evolution of polygyny and sexual dimorphism are largely derived from data on passerine birds. These models are less appropriate for taxa such as mammals, in which males emphasize mating strategies, than for those such as passerines, in which males emphasize progeny rearing strategies. The Orians-Verner model is inadequate as a general explanation of the evolution of polygyny in mammals because many species do not meet one or more of its assumptions: that the need for male parental care is the main factor opposing the evolution of polygyny; that females choose to mate with particular males; and that the female raises her young on the resources contained in the territory of the male with which she mates. A two-factor model incorporating the concept of sexual bimaturism, developed by Wiley for grouse, is more appropriate for many mammals but still too simple. In mammals, large male parental investment is a good predictor of both monogamy and reduced sexual dimorphism, but small male investment is a poor predictor of extreme polygyny and increased sexual dimorphism. Thus, large male parental investment is only one of the important factors which oppose the evolution of polygyny. An adequate mammalian model will have to include another set of factors which oppose the evolution of polygyny by increasing the spacing or mobility of females. It will also have to explain why sexual dimorphism has evolved more frequently in large mammals than in small ones. Sexual selection cannot account for all the variation in degree of sexual dimorphism found in mammals. An emerging paradigm based on the consideration of bioenergetic constraints and the factors affecting female size promises new insight.

Conservation biology: Inbreeding leads to extinction

Opinion on the question of whether genetic problems such as inbreeding contribute to the extinction of wild populations has been divided between two camps. On the one hand, inbreeding reduces reproductive success but, on the other hand, environmental events could causes extinctions before genetic factors come into play. The debate has now been resolved by a study of a wild butterfly population in Finland — and the evidence weighs down in favour of a significant role for inbreeding in the extinction of wild populations.

A noninvasive method for distinguishing among canid species: amplification and enzyme restriction of DNA from dung.

Endangered San Joaquin kit foxes Vulpes macrotis mutica can be sympatrically distributed with as many as four other canids: red fox, gray fox, coyote and domestic dog. Canid scats are often found during routine fieldwork, but cannot be reliably identified to species. To detect and study the endangered kit fox, we developed mitochondrial DNA markers that can be amplified from small amounts of DNA extracted from scats. We amplified a 412‐bp fragment of the mitochondrial cytochrome‐b gene from scat samples and digested it with three restriction enzymes. The resulting restriction profiles discriminated among all five canid species and correctly identified 10 ‘unknown’ fox scats to species in blind tests. We have applied our technique to identify canids species for an environmental management study and a conservation study. We envision that our protocol, and similar ones developed for other endangered species will be greatly used for conservation management in the future.

Predation on San Joaquin Kit Foxes by Larger Canids

A better understanding of the relationships between endangered San Joaquin kit foxes ( Vulpes macrotis mutica ) and sympatric larger canids that prey on them is important for conservation efforts toward kit foxes. We used radiotelemetry to monitor the survival and cause of death of 41 San Joaquin kit foxes and 24 coyotes ( Cants latrans ) on the Carrizo Plain Natural Area, California, during the 1989–1991 drought. The estimated minimum-annual-survival rate for all coyotes was 0.88. Estimated annual-survival rates for juvenile foxes (0.21–0.41) were somewhat less than those for adult foxes (0.58–0.61). Survival rates for foxes were similar across years and sexes. Larger canids accounted for 78% of 23 verified deaths of kit foxes: 15 killed by coyotes; 2 by non-native red foxes ( Vulpes vulpes ); 1 by a domestic dog. High predation by larger canids, coupled with poor reproduction in kit foxes due to reduced prey availability during the drought, contributed to a significant decrease in density of kit foxes (from 0.24 to 0.12 foxes/km2) during the study. Although coyotes can have a significant impact on populations of kit foxes, larger non-native red foxes may pose a greater threat in some areas.

Detection and accuracy rates of dogs trained to find scats of San Joaquin kit foxes (Vulpes macrotis mutica)

Specially trained detection dogs have been used to locate faeces (scats) for faecal analyses but their effectiveness has not been quantified. We evaluated detection and accuracy rates of dogs trained to find scats of endangered San Joaquin kit foxes (Vulpes macrotis mutica). Four dogs found from 0.43 to 5.37 presumptive kit fox scats per km of transect searched in two field sites where kit foxes and coyotes (Canis latrans) but not non-native red foxes (V. vulpes) were present. The unusually low detection rate (0.43 scats per km) by one dog (probably due to excessive panting in hot weather) was still similar to the average scat detection rate of two experienced humans. DNA tests of 1298 scats showed that all dogs were 100% accurate at distinguishing kit fox scats under our field conditions. Because red foxes are sympatric with kit foxes in some areas, we also conducted controlled discrimination experiments to see if trained dogs could distinguish between scats from kit and red foxes. Four dogs were 100% accurate at choosing a kit fox scat when red fox scats were present (n = 64 trials), but were less accurate at ignoring red fox scats in trials where a kit fox scat was absent.

Captive breeding programs for populations with a small number of founders.

Small captive populations are likely to become extinct. Detailed breeding plans based on the principles of population genetics and demography can greatly increase their chances of long-term survival. Zoos have now begun to implement such plans but lack the resources to extend them to the many species that are likely to become extinct in the wild in the near future.

Saving the Vaquita: Immediate Action, Not More Data

∗Instituto Nacional de Ecolog ?a (INE), c/o CICESE, Km. 107 Carretera EnsenadaTijuana, Ensenada, BC 22860, Mexico †Instituto Nacional de Ecolog ?a (INE), c/o CICESE, Km. 107 Carretera EnsenadaTijuana, Ensenada, BC 22860, Mexico ‡Southwest Fisheries Science Center, 8604 La Jolla Shores Drive, La Jolla, CA 92038, U.S.A. ∗∗Duke University Marine Laboratory, Nicholas School of the Environment, 135 Duke Marine Laboratory Road, Beaufort, NC 28516-9721, U.S.A. ††Okapi Wildlife Associates, 27 Chandler Lane, Hudson, Quebec JOP-1HO, Canada ‡‡National Zoological Park, Smithsonian Institution, P.O. Box 37012 MRC 5503, Washington, D.C. 20013-7012, U.S.A. §Southwest Fisheries Science Center, 8604 La Jolla Shores Drive, La Jolla, CA 92038, U.S.A. This paper is posted at DigitalCommons@University of Nebraska Lincoln.

Inbreeding and juvenile mortality in small populations of ungulates: A detailed analysis

Juvenile mortality of inbred young was higher than that of noninbred young in 15 of 16 species of captive ungulates. In 19 of 25 individual females, belonging to ten species, a larger percentage of young died when the female was mated to a related male than when she was mated to an unrelated male.