Estimated Sex Ratio Research Articles

POPULATION BIOLOGY OF CHAMAELIRIUM LUTEUM, A DIOECIOUS LILY. II. MECHANISMS GOVERNING SEX RATIOS.

The evolution of sex ratios has long been a focus of scientific interest (Darwin, 1871; Fisher, 1930). Many theoretical studies have shown that a one to one primary (zygotic) sex ratio is to be expected in most cases (Fisher, 1930; Shaw and Mohler, 1953; Bodmer and Edwards, 1960; Kolman, 1960; Leigh, 1970; Charnov, 1975; Eshel, 1975). This expectation is based on the fact that in a dioecious sexually reproducing population, each offspring produced will contain equal gene complements from male and female parents. If there is an excess of one sex in the population, the fitness of individuals of the opposite sex will increase, and mutations resulting in an increase in numbers of that opposite sex will be favored by selection. By this mechanism, primary sex ratios are expected to be kept in an evolutionary balance near one to one. However, observations of secondary (adult) sex ratios in many animal and plant species show an excess of one sex or the other (Davey and Gibson, 1917; Correns, 1928; Godley, 1964, 1976; Hamilton, 1967; Harris, 1968; Zarzycki and Rychlewski, 1972; Lloyd, 1973; Richards, 1975; Barlow and Wiens, 1976; Melampy and Howe, 1977; Opler and Bawa, 1978; Werren and Charnov, 1978). Skewed secondary sex ratios could be the result of genetic mechanisms which bring about unequal numbers of male and female progeny (i.e., skewed primary sex ratios); or, alternatively, they could be the result of post-zygotic life history differences between males and females. The dioecious perennial forest floor herb Chamaelirium luteum (L.) Gray (Liliaceae) has been studied extensively with respect to spatial distributions of males and females (Meagher, 1980) and life history differences between the sexes (Meagher and Antonovics, in press). Plants of this species are constant over time with respect to sex expression; there have been no sex changes observed over the seven years of this study (Meagher, 1980). A particularly striking feature of this species, noted in these earlier studies and in Radford et al. (1968), is that sex ratios in natural populations always show a strong excess of males. However, such observations on the sex ratio are limited in that often only a fraction of the plants present will be in flower in a particular year, so that the sex ratio estimate could be strongly influenced by differences between the sexes in flowering schedules (e.g., Vernet, 197 1). In a perennial species such as C. luteum, the sex ratio may be regarded at three levels: 1) the seedling (primary) sex ratio, 2) the adult (secondary) sex ratio, and 3) the sex ratio among plants in flower in any given year (flowering sex ratio). The study presented here was undertaken to answer the following questions. Do the seedling, flowering or adult sex ratios of C. luteum show a bias towards males or females? How are these different sex ratio estimates interrelated? Finally, what influence do various factors, such as genetic mechanisms or ecological and life history differences between the sexes, have on adult sex ratios?

Sex-Ratio Estimation, Sequential Sampling, and the Programmable Pocket Calculator

Determination of sex-ratios associated with large numbers of insects (trap catch, quadrat samples, etc.) is a recurrent problem in entomological research, frequently involving tedious microscopic examination of individuals. Considerable savings in time and money may result from use of an appropriately designed sequential sampling procedure for estimating sex-ratio. Sequential sampling has enjoyed a deserved popularity in recent years (e.g., see Gonzalez 1970), a3 an efficient means of estimating infestation levels of pest populations with regard to their location above or below a critical value (usually the economic threshold). The basic techniques for this type of sequential sampling (reviewed by Waters 1955) are, however, inappropriate for sex-ratio estimation.

EARLY DIFFERENTIAL MORTALITY IN NEODIPRION SERTIFER (HYMENOPTERA: DIPRIONIDAE)

AbstractIn Neodiprion sertifer (Geoff.), mortality is greater in males than in females in the egg stage and probably also among early larvae, but in the late larval period females are more susceptible. The evidence consists of the difference in mortality between all-male and mixed (male + female) colonies, as well as the relationship of secondary sex ratio to preceding mortality and the number of survivors per colony. The effect of differential mortality on estimation of the primary sex ratio is discussed.

Gill Net Selection, Migration, Size and Age Composition, Sex Ratio, Harvest Efficiency, and Management of Striped Bass in the Roanoke River, North Carolina

This study is based on about 5,000 striped bass collected from the Roanoke River in the springs of 1963, 1964, and 1965. The relation between gill net mesh size and the mean length of male striped bass caught is linear and is described by Y = 3.41X + 2.24 inches where Y = fork length in inches and X = stretched mesh size in inches. The girth-length relation for each sex is linear, and there is no significant difference be- tween sexes. It is described by Y = 0.67X - 1.12 inches, where Y = gill girth in inches and X = fork length in inches. Most males migrated upstream through Williamston between 26 March and 20 April; most females migrated through between 16 April and 12 May. Dominant age groups were III and IV for the males and IV and V for the females. Estimates of the mean fork lengths are: Males; 111-16.7 inches and IV-18.3 inches. Females; IV-20.2 inches and V-21.4 inches. Estimates of sex ratios from striped bass caught in gill nets in 1963-65 were 69.7%, 85.1%, and 76.9% males. The accuracy of these estimates is unknown. The large differences in the sex ratio estimates between years probably resulted from variation in recruitment into the Roanoke River population each year. The management techniques which are most feasible for increasing the value of the sport and commercial striped bass fisheries in North Carolina appear to be (1) increasing the mini- mum size limit from 12 inches total length to 16 inches fork length and (2) enforcing regu- lations which restrict the use of gill nets having mesh sizes under 4.75 inches stretched mesh.

The Influence of Sampling Methods on the Estimation of Population Structure in Painted Turtles

A natural population of painted turtles [Chrysemys picta (Schneider)] was studied in University Bay of Lake Mendota, Dane County, Wisconsin, from September 1960 to October 1962. Five methods were used to capture turtles for marking, measurement, and release. Each of the methods yielded a different size-class distribution and a sex ratio which, in four out of five cases, was significantly different from that of the total population estimate. Baited hoop nets yielded predominantly males and relatively few juveniles; basking traps tended to yield higher percentages of females than did nets, and large turtles were an important component of the sample. Hand capture resulted in a sample heavily weighted by juveniles and a 1: 1 sex ratio for adults. The influence of trapping method in the estimation of population structure in turtles must not be overlooked. This study indicates that even within a species, trapping method introduces considerable bias in the estimation of sex ratio and size-class distribution. INTRODUCTION The structure of turtle populations, as estiimated by different authors (Cagle, 1942, 1944, 1954; Pearse, 1923; Sexton, 1959), has varied considerably even within the same species. Although this variation may be due to inherent differences in the populations studied, or to various ecological factors affecting each population with different intensities, it is more probable that the disparity lies in the sampling method used by the investigators. Cagle and Chaney (1950) suggested that sampling methods are biased by the behavioral patterns of the size classes and sexes that make up the population, but we are unaware of any study that has compared the variation in estimation of population and its strutcture brought about by use of different sampling methods. A natural population of Chrysemys picta (Schneider) was studied in University Bay of Lake Mendota, Dane County, Wisconsin, from September 1960 to October 1962. The central painted turtle, Chrysemys picta marginata (Agassiz) and the western painted turtle, Chrysemys picta belli (Gray) intergrade in this region (Pope, 1949). Five methods were used to capture a maximum number of turtles for marking, measurement, and release. Variant results obtained from use of these methods were sufficiently striking to, warrant a comparison of the methods. Acknowledgments.-This study was done with the aid of two NSF Summer Fellowships for Teaching Assistants. Additional financial assistance for field equipment and limited field assistance was provided by a grant to Dr. W. G. Reeder from the Wisconsin Alumni Research Foundation through the University of Wisconsin Graduate School. Appreciation for encouragement and constructive criticism is given to Dr. W. G. Reeder, Dr. J. M. Legler, and Dr.

A Method for Estimating Fall Adult Sex Ratios from Production and Survival Data

This paper presents a method of utilizing data relating to the production and survival of a bird population to estimate a basic fall adult sex ratio. This basic adult sex ratio is an average value derived from average production and survival rates. It is an estimate of the average sex ratio about which the fall adult ratios will fluctuate according to annual variations in production and survival. The basic fall adult sex ratio has been calculated as an asymptotic value which is the limit of an infinite series wherein average population characteristics are used as constants. Graphs are provided that allow the determination of basic sex ratios from production and survival data of a population. Where the respective asymptote has been determined, it may be possible to estimate various production and survival rates by use of variations of the formula for estimating the asymptote. The problem of determining a fall adult sex ratio of a bird population has many pitfalls if the data are derived from such sources as wing surveys, bag checks, breeding population surveys, or trapped birds. Corrections must be made for such potential sources of bias as these: differential vulnerability to the gun; unequal trapping success for one sex rather than the other; differences in behavior or coloration that make one sex more readily observed than the other. The purpose of this paper is to pr sent a method that permits the estimat on of adult sex ratios using production and survival data. It might appear that if the annual average survival rate of males in a population is greater than the female rate, the sex ratio of the population would increasingly favor the males, with a possible detriment to the pop1 Present address: Department of Fisheries and Wildlife, Oregon State University, Corvallis. 185 ROBBINS, C. S. 1960. Woodcock status report1960. U. S. Fish and Wildl. Serv. Spec. Sci. Rept.-Wildl. 50. 26pp. SHELDON, W. G. 1961. Summer crepuscular flights of American woodcocks in central Massachusetts. Wilson Bull. 73(2):126-139. --, F. GREELEY, AND J. KUPA. 1958. Aging fall-shot American woodcocks by primary wear. J. Wildl. Mgmt. 22(3):310-312. WALLACE, G. J. 1962. The seventh spring dieoff of robins at East Lansing, Michigan. The Jack-Pine Warbler 40(1):28-32. , AND R. F. BERNARD. 1963. Tests show 40 species of birds poisoned by DDT. Audubon Magazine 65(4):195-203. 1, A. C. ETTER, AND D. R. OSBORNE. 1964. Spring mortality of birds following fall spraying of elms. Massachusetts Audubon 48(3): 116-120. WEBB, F. E., J. R. BLAIS, AND R. W. NASH. 1961. A cartographic history of spruce budworm outbreaks and aerial forest spraying in the Atlantic region of North America, 1949-1959. Canadian Entomol. 93(5):360-379. WRIGHT, B. S. 1952. Woodcock banding with bird dogs. Pages 45-46. In Aldrich, J. W., and others, Investigations of woodcock, snipe, and rails in 1951. U. S. Fish and Wildl. Serv. and Canadian Wildl. Serv. Spec. Sci. Rept.Wildl. 14. 58pp. 1960. Woodcock reproduction in DDTsprayed areas of New Brunswick. J. Wildl. Mgmt. 24(4):419-420. Received for publication May 19, 1964. This content downloaded from 157.55.39.17 on Wed, 31 Aug 2016 05:15:56 UTC All use subject to http://about.jstor.org/terms 186 Journal of Wildlife Management, Vol. 29, No. 1, January 1965 ulation as a whole. This subject has been mentioned by William R. Hanson (Calculation of productivity, survival, and abundance of selected vertebrates from sex and age ratios. Wildl. Monographs 9. 60pp. 1963). He states, Unequal numbers of sexes among mature animals tend to be equalized by the addition of the next crop of subadults if the sex ratio of subadults is approximately (Hanson 1963:11). We will expand the treatment of the subject to show that under most conditions the sex ratio of adults tends to stabilize, even though the sex ratio of subadults is not

Mass Spawning Behavior of Sockeye Salmon in Brooks River, Alaska

The spawning behavior of sockeye salmon in Brooks River, Alaska, was studied in 1957 and 1958. In both years, 3 successive waves of spawners occupied the gravels. Males spent about 5 days on the redd sites and females about 9 days. Both sexes dug redds, but females were considerably more vigorous and effective. Males defended spawning territories vigorously, but almost entirely against other males. Females defended territories against both males and females. When the male of a spawning pair disappeared, the female defended the redd against fish of either sex. Defense of the redd has obvious survival value if successive spawning reduces overall egg survival as a result of excavation of previously deposited eggs. Differences in the life-spans of males and females may cause erroneous estimates of sex ratios if counts are made of only the live or the dead fish during the spawning period.

Estimation of Sex Ratio in a Series of Excavated Skeletal Materials

Introduction. Some thirty human skeletal remains, together with artifacts of the Okhotsk type (approx. A. D. 1000), were discovered at Omisaki in the northernmost part of the Okhotsk coast in Hokkaido. The remains were excavated by workmen; but were deposited in boxes and reburied at another site, according to ordinary cus tom, Shortly thereafter, the boxes in which the bones had been placed in a random order were re-excavated by the author. Such being the circumstances, it was exceedingly difficult to identify the individual skeletal sets. Thus our attention was shifted to the statistical study of each bone series rather than the study of individual skeletal sets. The most difficult point in the anthropological investigation of this material was the determination of the sex of each bone. If the individual set of skeleton had been preserved, the sex could have read ilybeen estimated by observing the skull and the pelvis or some coexisting artifacts. However, under such unfavorable conditions, we were forced, for instance, to identify the sex of the tibia quite separately from that of the femur.