Populations of Alsophila pometaria (Harris) are largely gynogenetic and composed of asexual females that must mate with a conspecific male to reproduce. Within this asexual contingent, there are a variety of electrophoretically defined multilocus genotypes. In this study we found that populations differ in sex ratio. We also found that there is an indication of differential mating success among asexual genotypes in a population of A. pometaria

Futuyma, Douglas J.

Harshman, Lawrence G.

English

DigitalCommons@University of Nebraska

University of Nebraska - LincolnDigitalCommons@University of Nebraska - LincolnLawrence G. Harshman Publications Papers in the Biological Sciences7-1985Variation in Population Sex Ratio and MatingSuccess of Asexual Lineages of Alsophila pometaria(Lepidoptera: Geometridae)Lawrence G. HarshmanUniversity of Nebraska–Lincoln, lharshman1@unl.eduDouglas J. FutuymaState University of New York at Stony Brook, douglas.futuyma@stonybrook.eduFollow this and additional works at: http://digitalcommons.unl.edu/biosciharshmanPart of the Entomology Commons, and the Genetics CommonsThis Article is brought to you for free and open access by the Papers in the Biological Sciences at DigitalCommons@University of Nebraska - Lincoln.It has been accepted for inclusion in Lawrence G. Harshman Publications by an authorized administrator of DigitalCommons@University of Nebraska- Lincoln.Harshman, Lawrence G. and Futuyma, Douglas J., "Variation in Population Sex Ratio and Mating Success of Asexual Lineages ofAlsophila pometaria (Lepidoptera: Geometridae)" (1985). Lawrence G. Harshman Publications. 8.http://digitalcommons.unl.edu/biosciharshman/8   Published in Annals of the Entomological Society of America 78:4 (July 1985), pp. 456–458; doi: http://0-dx.doi.org.library.unl.edu/10.1093/aesa/78.4.456. Copyright © 1985 Entomological Society of America. Used by permission. Submitted November 8, 1984; accepted March 5, 1985.   Variation in Population Sex Ratio and Mating Success of Asexual Lineages of Alsophila pometaria (Lepidoptera: Geometridae)   Lawrence G. Harshman1 and Douglas J. Futuyma  Department of Ecology and Evolution, State University of New York at Stony Brook, Stony Brook, New York 11794  Abstract Populations of Alsophila pometaria (Harris) are largely gynogenetic and composed of asexual females that must mate with a conspecific male to reproduce. Within this asexual contingent, there are a variety of electrophoretically defined multilocus genotypes. In this study we found that populations differ in sex ratio. We also found that there is an indication of differential mating success among asexual genotypes in a population of A. pometaria.  Gynogenesis is an unusual form of reproduction in which asexual females must mate be-fore reproducing, but males make no genetic contribution to the offspring. Gynogenetic females of Alsophila pometaria (Harris), the fall cankerworm, pass on their genotype intact to progeny yet must mate with a conspecific male to reproduce (Mitter and Futuyma 1977). Electrophoretic surveys and breeding studies have shown that there are a variety of asex-ual genotypes (clones) within populations of this species (Mitter et al. 1979, Harshman 1982). Sexual reproduction is also present and sexual females are assumed to be the source of males upon which gynogenetic females depend (Mitter et al. 1979, Harshman 1982). The population sex ratio of the fall cankerworm is female-biased (Porter and Alden 1924, Balch 1938, Mitter et al. 1979), reflecting the preponderance of asexual reproduction. In this study we have surveyed local populations for variation in sex ratio. Male abun-dance is a critical parameter in gynogenetic populations (Kiester et al. 1981), particularly H A R S H M A N  A N D  F U T U Y M A ,  A N N A L S  O F  T H E  E N T O M O L O G I C A L  S O C I E T Y  O F  A M E R I C A  7 8  (1 9 8 5 )  2 so where sex ratios are extreme and many females go unmated. We also studied whether or not there was differential mating success among the asexual lineages found in popula-tions of the fall cankerworm. Gynogenetic species may often be composed of a variety of asexual genotypes (Vrijenhoek 1979, Mitter et al. 1979), and where males are in short sup-ply, mating success could be an important component of fitness of asexual lineages.  Materials and Methods  Population Sex Ratio On Long Island, New York, eggs of the univoltine fall cankerworm hatch in late April and early May. Larvae are polyphagous and usually found feeding on the foliage of deciduous tress. Pupation occurs in the soil, where there is an obligate summer diapause. In the last week of May 1981, late-instar larvae were collected from seven sites by striking vegetation over a beating net. Samples were brought into the laboratory and larvae were fed oak leaves (Quercus coccinea and Quercus velutina) until they were ready to pupate (usually within a week). There was little mortality in the laboratory and prepupae were placed in a mixture of sterilized sand and potting soil. After 2 months the subterranean cocoons were unearthed and pupae extracted. Male and female pupae could be distinguished by differ-ences in body shape, genital pore position, and wing development. It is difficult to devise an unbiased sampling procedure for adults because the females are wingless and the males fly. Consequently, it seems likely that our method of determining population sex ratio from collections of larvae is more accurate than counting or trapping adults in the field. All the collection sites were on Long Island (fig. 1). The north shore of the island gener-ally has mesic habitat dominated by species of the red oak group (subgenus Eryth-robalanus) and red maple (Acer rubrum). This includes the Graduate Biology and Ashley Schiff sites, which are on the Stony Brook campus of the State University of New York, and the Village Wood site, which is located several kilometers away in the village of Stony Brook. Belmont State Park and Southern State Parkway are near the southern shore of the middle of Long Island. The Belmont State Park site is mesic and characterized by trees of the red oak group and red maple. The Southern State Parkway site is drier and dominated by white oak (Quercus alba) and scrub oak (Q. ilicifolia). The remaining two locations are in the sandy outwash plain that makes up much of the southeastern portion of the island. One of these locations, Route 27, is almost entirely composed of scrub oak and stunted pitch pine (Pinus rigida). The other, called Low Planes, is similar but has several additional oak species.   H A R S H M A N  A N D  F U T U Y M A ,  A N N A L S  O F  T H E  E N T O M O L O G I C A L  S O C I E T Y  O F  A M E R I C A  7 8  (1 9 8 5 )  3   Figure 1. Alsophila pometaria collection sites on Long Island, New York.  Mating Success Adults of the fall cankerworm emerge on Long Island in the late fall or early winter. Fe-males are wingless and may be found on tree trunks, apparently releasing pheromone to attract males flying in the vicinity. Mating may last for several hours, and immediately after it is terminated females climb into the canopy to deposit their eggs. Mating success, in the context of this investigation, refers to female attainment of copulation. In 1980, moths were collected in the Ashley Schiff site. Most were taken from 7:00 p.m. until 11:00 p.m. on the evening of 1 December. The first week in December was the mating window for adults of that generation because there were few other periods with tempera-tures high enough for males to fly. Many females with eggs were found on tree trunks throughout the early winter, and they presumably went unmated. On 1 December un-mated and mating moths were collected at the same time. Each mating pair was transferred with soft forceps into a cardboard container. The offspring of most of these females were electrophoretically tested to determine the maternal mode of reproduction. It was possible to determine which females had not mated because they were not climbing upward and were usually in a characteristic posture they presumably assume to release pheromones. Where possible, the nearest unmated female on the same tree as a mating pair and an un-mated female from the nearest tree were also collected. This pattern of sampling was em-ployed to look for differences between mated and unmated females on a relatively fine spatial scale. All females were frozen and analyzed by electrophoresis, using the tech-niques of Mitter et al. (1979) and modifications of Futuyma et al. (1981). In this manner, a four-locus genotype was determined for each individual.   H A R S H M A N  A N D  F U T U Y M A ,  A N N A L S  O F  T H E  E N T O M O L O G I C A L  S O C I E T Y  O F  A M E R I C A  7 8  (1 9 8 5 )  4 Results  Population Sex Ratio The locations in table 1 are arranged in increasing order of male proportion, and it is clear that males made up a small percentage of these populations. It also appears that the sex ratio can vary over relatively short distances. For instance, collections from the three sites on the north shore varied in male proportion from 0.015 to 0.057, and Low Planes had a higher frequency of males than nearby Route 27. On the other hand, the two sites from the mid-island south shore (locations 1 and 2) had a similar proportion of males. A test of independence shows that there was overall heterogeneity among sites in population sex ratio (G = 17.940, P < 0.01). However, none of the pairwise comparisons between popula-tions were significant when unplanned a posteriori tests were conducted using a conserva-tive α obtained by dividing the standard significance level by the number of possible pairwise tests.  Table 1. Male proportion in Long Island sites Location Male proportion n Route 27 0.011 87 Village Wood 0.015 227 Ashley Schiff 0.029 103 Graduate Biology 0.057 210 Belmont State Park 0.063 756 Southern State Parkway 0.066 411 Low Planes 0.067 750  Mating Success The multilocus genotype of 70% of all females collected from the Ashley Schiff population matched that of previously identified clones (Harshman 1982). In addition, an electropho-retic progeny analysis of 90 of the mated females collected on 1 December 1980 revealed that only one was sexual (Harshman and Futuyma 1985). Therefore, it seems reasonable to assume that almost all the unmated females collected in the Ashley Schiff site were asexual. Table 2 shows the genotypes categorized on the basis of abundance. The letter portion of the designation of five common genotypes is from Mitter et al. (1979) and Futuyma et al. (1981), and the corresponding number from Harshman (1982). Clones 1(C), 2(B), 8(Y), 26(A), and 48(Z) each made up at least 5% of the total number of females collected. The “infrequent” group was made up of a few genotypes that made up between 1 and 5% of the sample. The “uncommon” genotypes were mostly unique in the sample and made up less than 1% of the total.   H A R S H M A N  A N D  F U T U Y M A ,  A N N A L S  O F  T H E  E N T O M O L O G I C A L  S O C I E T Y  O F  A M E R I C A  7 8  (1 9 8 5 )  5 Table 2. Female mating success in the Ashley Schiff population of Alsophila pometaria Genotype group % Mated No. of females 8(Y) 52.5 40 2(B) 47.5 34 26(A) 40.0 20 48(Z) 28.6 28 1(C) 16.7 18 Infrequent 52.9 17 Uncommon 33.3 45  The percentage of females that were mated ranged from 52.9% for the “infrequent” group to 16.7% for clone 1(C). A statistical analysis was conducted to determine if there was a significant difference between genotype groups in the frequency of mating and non-mating females. The results of a test of independence are marginal (G = 11.428, P = 0.08) but suggest the presence of an overall difference in mating success among asexual geno-types.  Discussion  Gynogenesis is found sporadically in animal taxa. In the insects a ptinid beetle (Moore et al. 1956), delphacid leafhopper (Drosopoulos 1976), psychid moth (Narbel-Hofstetter 1955, 1963), and the fall cankerworm are known to be gynogenetic. Factors such as male prefer-ence for sexual females must be in operation for coexistence between gynogens and bisex-uals because of the reproductive advantage the asexual contingent enjoys (Moore 1976, Kiester et al. 1981). We were not able to determine if males prefer sexual females because the latter were rare in the Ashley Schiff site. However, allele frequencies from Ashley Schiff males can be used to determine the frequency that any sexual genotype will appear in the population. These calculations reveal that even the most likely sexual genotype will be classified as uncommon (Harshman 1982). In the present study there is no evidence that uncommon female genotypes have a mating advantage (see table 2). Thus, there is no evi-dence for frequency-dependent mating success, which would favor sexual lineages and promote the coexistence of sexual and asexual reproduction. We have found that populations of A. pometaria are highly female-biased. There is geo-graphic variation in sex ratio, and in some populations males are rare. Thus, it is likely that females often go unmated and asexual lineages compete for limited male reproductive function. In the Ashley Schiff population there was evidence for differential mating success among asexual lineages of A. pometaria. Females of clone 1(C) were particularly unsuccess-ful in obtaining a mating. It has been observed that larvae of this genotype are more likely to undergo density-dependent melanization than are larvae of other common clones (Fu-tuyma et al. 1981). Melanization results in faster larval development and lower adult weight (Schneider 1979, Futuyma et al. 1981), and smaller females were less likely to obtain a mating in a preliminary laboratory experiment (Harshman 1982). Thus, a propensity to melanize may have resulted in lower mating success for clone 1(C). Similarly, attributes of H A R S H M A N  A N D  F U T U Y M A ,  A N N A L S  O F  T H E  E N T O M O L O G I C A L  S O C I E T Y  O F  A M E R I C A  7 8  (1 9 8 5 )  6 other asexual genotypes, such as relative time of adult eclosion (Mitter et al. 1979), may affect mating success in populations of the fall cankerworm.  Acknowledgments – We express our appreciation to Richard Koehn for generously providing facil-ities for electrophoresis. We also thank Jerry Hilbish for assistance in the field. This is Contribution No. 525 from the Program of Ecology and Evolution at the State University of New York at Stony Brook. This research was supported by grants from the National Science Foundation (BSR 8306000) and the Whitehall Foundation.  Note 1. Current address: Department of Genetics, University of California at Davis, Davis, CA 95616.  References Cited  Balch, R. E. 1938. Further notes on the fall cankerworm and its control by “solid-stream” spraying. Sci. Agric. 19: 411–423. Drosopoulos, S. 1976. Triploid pseudogamous biotype of the leafhopper Muellerianella fairmairei. Na-ture (London) 263: 499–500. Futuyma, D. J., S. L. Leipertz, and C. Mitter. 1981. Selective factors affecting clonal variation in the fall cankerworm, Alsophila pometaria (Lepidoptera: Geometridae). Heredity 47: 161–172. Harshman, L. H. 1982. Studies on the ecology and genetics of Alsophila pometaria (Lepidoptera: Ge-ometridae). PhD dissertation, State University of New York at Stony Brook. Harshman, L. H., and D. J. Futuyma. 1985. The origin and distribution of clonal diversity in Alsophila pometaria (Lepidoptera: Geometridae). Evolution (in press). Kiester, A. R., T. Nagylaki, and B. Schaeffer. 1981. Population dynamics of species with gynogenetic sibling species. Theor. Popul. Biol. 19: 358–369. Miner, C., and D. J. Futuyma. 1977. Parthenogenesis in the fall cankerworm, Alsophila pometaria (Lep-idoptera: Geometridae). Entomol. Exp. Appl. 21: 192–198. Mitter, C., D. J. Futuyma, J. C. Schneider, and J. D. Hare. 1979. Genetic variation and host plant rela-tions in a parthenogenetic moth. Evolution 33: 777–790. Moore, B. P., C. E. Woodroffe, and A. R. Sanderson. 1956. Polymorphism and parthenogenesis in a ptinid beetle. Nature (London) 177: 847–848. Moore, W. S. 1976. Components of fitness in the unisexual fish Poedliopsis monacha-occidentalis. Evo-lution 30: 564–578. Narbel-Hofstetter, M. 1955. La pseudogamie chez Luffia lapidella Geoze (Lepid. Psychidae). Rev. Suisse Zool. 62: 224–229. ―—. 1963. Cytologie de la pseudogamie chez Luffia lapidella Geoze (Lepid. Psychidae). Chromosoma 13: 623–645. Porter, G. A., and C. H. Alden. 1925. The cankerworms. U.S. Dep. of Agric. Bull. 1238: 1–37. Schneider, J. C. 1979. Phenological and kentromorphic aspect of the population ecology of the fall cankerworm Alsophila pometaria (Lepidoptera: Geometridae). PhD dissertation, Princeton Univer-sity, Princeton, NJ. Vrijenhoek, R. C. 1979. Factors affecting clonal diversity and coexistence. Am. Zool. 19: 787–797. 

Variation in Population Sex Ratio and Mating Success of Asexual Lineages of \u3ci\u3eAlsophila pometaria\u3c/i\u3e (Lepidoptera:
Geometridae)

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University of Nebraska - Lincoln
DigitalCommons@University of Nebraska - Lincoln
Lawrence G. Harshman Publications Papers in the Biological Sciences
7-1985
Variation in Population Sex Ratio and Mating
Success of Asexual Lineages of Alsophila pometaria
(Lepidoptera: Geometridae)
Lawrence G. Harshman
University of Nebraska–Lincoln, lharshman1@unl.edu
Douglas J. Futuyma
State University of New York at Stony Brook, douglas.futuyma@stonybrook.edu
Follow this and additional works at: http://digitalcommons.unl.edu/biosciharshman
Part of the Entomology Commons, and the Genetics Commons
This Article is brought to you for free and open access by the Papers in the Biological Sciences at DigitalCommons@University of Nebraska - Lincoln.
It has been accepted for inclusion in Lawrence G. Harshman Publications by an authorized administrator of DigitalCommons@University of Nebraska
- Lincoln.
Harshman, Lawrence G. and Futuyma, Douglas J., "Variation in Population Sex Ratio and Mating Success of Asexual Lineages of
Alsophila pometaria (Lepidoptera: Geometridae)" (1985). Lawrence G. Harshman Publications. 8.
http://digitalcommons.unl.edu/biosciharshman/8
 
 
 
Published in Annals of the Entomological Society of America 78:4 (July 1985), pp. 456–458; 
doi: http://0-dx.doi.org.library.unl.edu/10.1093/aesa/78.4.456. 
Copyright © 1985 Entomological Society of America. Used by permission. 
Submitted November 8, 1984; accepted March 5, 1985. 
 
 
Variation in Population Sex Ratio and 
Mating Success of Asexual Lineages of 
Alsophila pometaria (Lepidoptera: 
Geometridae) 
 
 
Lawrence G. Harshman1 and Douglas J. Futuyma 
 
Department of Ecology and Evolution, State University of New York at Stony Brook, Stony Brook, 
New York 11794 
 
Abstract 
Populations of Alsophila pometaria (Harris) are largely gynogenetic and composed of asexual females 
that must mate with a conspecific male to reproduce. Within this asexual contingent, there are a 
variety of electrophoretically defined multilocus genotypes. In this study we found that populations 
differ in sex ratio. We also found that there is an indication of differential mating success among 
asexual genotypes in a population of A. pometaria. 
 
Gynogenesis is an unusual form of reproduction in which asexual females must mate be-
fore reproducing, but males make no genetic contribution to the offspring. Gynogenetic 
females of Alsophila pometaria (Harris), the fall cankerworm, pass on their genotype intact 
to progeny yet must mate with a conspecific male to reproduce (Mitter and Futuyma 1977). 
Electrophoretic surveys and breeding studies have shown that there are a variety of asex-
ual genotypes (clones) within populations of this species (Mitter et al. 1979, Harshman 
1982). Sexual reproduction is also present and sexual females are assumed to be the source 
of males upon which gynogenetic females depend (Mitter et al. 1979, Harshman 1982). The 
population sex ratio of the fall cankerworm is female-biased (Porter and Alden 1924, Balch 
1938, Mitter et al. 1979), reflecting the preponderance of asexual reproduction. 
In this study we have surveyed local populations for variation in sex ratio. Male abun-
dance is a critical parameter in gynogenetic populations (Kiester et al. 1981), particularly 
H A R S H M A N  A N D  F U T U Y M A ,  A N N A L S  O F  T H E  E N T O M O L O G I C A L  S O C I E T Y  O F  A M E R I C A  7 8  (1 9 8 5 )  
2 
so where sex ratios are extreme and many females go unmated. We also studied whether 
or not there was differential mating success among the asexual lineages found in popula-
tions of the fall cankerworm. Gynogenetic species may often be composed of a variety of 
asexual genotypes (Vrijenhoek 1979, Mitter et al. 1979), and where males are in short sup-
ply, mating success could be an important component of fitness of asexual lineages. 
 
Materials and Methods 
 
Population Sex Ratio 
On Long Island, New York, eggs of the univoltine fall cankerworm hatch in late April and 
early May. Larvae are polyphagous and usually found feeding on the foliage of deciduous 
tress. Pupation occurs in the soil, where there is an obligate summer diapause. In the last 
week of May 1981, late-instar larvae were collected from seven sites by striking vegetation 
over a beating net. Samples were brought into the laboratory and larvae were fed oak 
leaves (Quercus coccinea and Quercus velutina) until they were ready to pupate (usually 
within a week). There was little mortality in the laboratory and prepupae were placed in a 
mixture of sterilized sand and potting soil. After 2 months the subterranean cocoons were 
unearthed and pupae extracted. Male and female pupae could be distinguished by differ-
ences in body shape, genital pore position, and wing development. It is difficult to devise 
an unbiased sampling procedure for adults because the females are wingless and the males 
fly. Consequently, it seems likely that our method of determining population sex ratio 
from collections of larvae is more accurate than counting or trapping adults in the field. 
All the collection sites were on Long Island (fig. 1). The north shore of the island gener-
ally has mesic habitat dominated by species of the red oak group (subgenus Eryth-
robalanus) and red maple (Acer rubrum). This includes the Graduate Biology and Ashley 
Schiff sites, which are on the Stony Brook campus of the State University of New York, and 
the Village Wood site, which is located several kilometers away in the village of Stony 
Brook. Belmont State Park and Southern State Parkway are near the southern shore of the 
middle of Long Island. The Belmont State Park site is mesic and characterized by trees of 
the red oak group and red maple. The Southern State Parkway site is drier and dominated 
by white oak (Quercus alba) and scrub oak (Q. ilicifolia). The remaining two locations are in 
the sandy outwash plain that makes up much of the southeastern portion of the island. 
One of these locations, Route 27, is almost entirely composed of scrub oak and stunted 
pitch pine (Pinus rigida). The other, called Low Planes, is similar but has several additional 
oak species. 
  
H A R S H M A N  A N D  F U T U Y M A ,  A N N A L S  O F  T H E  E N T O M O L O G I C A L  S O C I E T Y  O F  A M E R I C A  7 8  (1 9 8 5 )  
3 
 
 
Figure 1. Alsophila pometaria collection sites on Long Island, New York. 
 
Mating Success 
Adults of the fall cankerworm emerge on Long Island in the late fall or early winter. Fe-
males are wingless and may be found on tree trunks, apparently releasing pheromone to 
attract males flying in the vicinity. Mating may last for several hours, and immediately 
after it is terminated females climb into the canopy to deposit their eggs. Mating success, 
in the context of this investigation, refers to female attainment of copulation. 
In 1980, moths were collected in the Ashley Schiff site. Most were taken from 7:00 p.m. 
until 11:00 p.m. on the evening of 1 December. The first week in December was the mating 
window for adults of that generation because there were few other periods with tempera-
tures high enough for males to fly. Many females with eggs were found on tree trunks 
throughout the early winter, and they presumably went unmated. On 1 December un-
mated and mating moths were collected at the same time. Each mating pair was transferred 
with soft forceps into a cardboard container. The offspring of most of these females were 
electrophoretically tested to determine the maternal mode of reproduction. It was possible 
to determine which females had not mated because they were not climbing upward and 
were usually in a characteristic posture they presumably assume to release pheromones. 
Where possible, the nearest unmated female on the same tree as a mating pair and an un-
mated female from the nearest tree were also collected. This pattern of sampling was em-
ployed to look for differences between mated and unmated females on a relatively fine 
spatial scale. All females were frozen and analyzed by electrophoresis, using the tech-
niques of Mitter et al. (1979) and modifications of Futuyma et al. (1981). In this manner, a 
four-locus genotype was determined for each individual. 
  
H A R S H M A N  A N D  F U T U Y M A ,  A N N A L S  O F  T H E  E N T O M O L O G I C A L  S O C I E T Y  O F  A M E R I C A  7 8  (1 9 8 5 )  
4 
Results 
 
Population Sex Ratio 
The locations in table 1 are arranged in increasing order of male proportion, and it is clear 
that males made up a small percentage of these populations. It also appears that the sex 
ratio can vary over relatively short distances. For instance, collections from the three sites 
on the north shore varied in male proportion from 0.015 to 0.057, and Low Planes had a 
higher frequency of males than nearby Route 27. On the other hand, the two sites from the 
mid-island south shore (locations 1 and 2) had a similar proportion of males. A test of 
independence shows that there was overall heterogeneity among sites in population sex 
ratio (G = 17.940, P < 0.01). However, none of the pairwise comparisons between popula-
tions were significant when unplanned a posteriori tests were conducted using a conserva-
tive α obtained by dividing the standard significance level by the number of possible 
pairwise tests. 
 
Table 1. Male proportion in Long Island sites 
Location Male proportion n 
Route 27 0.011 87 
Village Wood 0.015 227 
Ashley Schiff 0.029 103 
Graduate Biology 0.057 210 
Belmont State Park 0.063 756 
Southern State Parkway 0.066 411 
Low Planes 0.067 750 
 
Mating Success 
The multilocus genotype of 70% of all females collected from the Ashley Schiff population 
matched that of previously identified clones (Harshman 1982). In addition, an electropho-
retic progeny analysis of 90 of the mated females collected on 1 December 1980 revealed 
that only one was sexual (Harshman and Futuyma 1985). Therefore, it seems reasonable to 
assume that almost all the unmated females collected in the Ashley Schiff site were asexual. 
Table 2 shows the genotypes categorized on the basis of abundance. The letter portion 
of the designation of five common genotypes is from Mitter et al. (1979) and Futuyma et 
al. (1981), and the corresponding number from Harshman (1982). Clones 1(C), 2(B), 8(Y), 
26(A), and 48(Z) each made up at least 5% of the total number of females collected. The 
“infrequent” group was made up of a few genotypes that made up between 1 and 5% of 
the sample. The “uncommon” genotypes were mostly unique in the sample and made up 
less than 1% of the total. 
  
H A R S H M A N  A N D  F U T U Y M A ,  A N N A L S  O F  T H E  E N T O M O L O G I C A L  S O C I E T Y  O F  A M E R I C A  7 8  (1 9 8 5 )  
5 
Table 2. Female mating success in the Ashley 
Schiff population of Alsophila pometaria 
Genotype group % Mated No. of females 
8(Y) 52.5 40 
2(B) 47.5 34 
26(A) 40.0 20 
48(Z) 28.6 28 
1(C) 16.7 18 
Infrequent 52.9 17 
Uncommon 33.3 45 
 
The percentage of females that were mated ranged from 52.9% for the “infrequent” 
group to 16.7% for clone 1(C). A statistical analysis was conducted to determine if there 
was a significant difference between genotype groups in the frequency of mating and non-
mating females. The results of a test of independence are marginal (G = 11.428, P = 0.08) 
but suggest the presence of an overall difference in mating success among asexual geno-
types. 
 
Discussion 
 
Gynogenesis is found sporadically in animal taxa. In the insects a ptinid beetle (Moore et 
al. 1956), delphacid leafhopper (Drosopoulos 1976), psychid moth (Narbel-Hofstetter 1955, 
1963), and the fall cankerworm are known to be gynogenetic. Factors such as male prefer-
ence for sexual females must be in operation for coexistence between gynogens and bisex-
uals because of the reproductive advantage the asexual contingent enjoys (Moore 1976, 
Kiester et al. 1981). We were not able to determine if males prefer sexual females because 
the latter were rare in the Ashley Schiff site. However, allele frequencies from Ashley Schiff 
males can be used to determine the frequency that any sexual genotype will appear in the 
population. These calculations reveal that even the most likely sexual genotype will be 
classified as uncommon (Harshman 1982). In the present study there is no evidence that 
uncommon female genotypes have a mating advantage (see table 2). Thus, there is no evi-
dence for frequency-dependent mating success, which would favor sexual lineages and 
promote the coexistence of sexual and asexual reproduction. 
We have found that populations of A. pometaria are highly female-biased. There is geo-
graphic variation in sex ratio, and in some populations males are rare. Thus, it is likely that 
females often go unmated and asexual lineages compete for limited male reproductive 
function. In the Ashley Schiff population there was evidence for differential mating success 
among asexual lineages of A. pometaria. Females of clone 1(C) were particularly unsuccess-
ful in obtaining a mating. It has been observed that larvae of this genotype are more likely 
to undergo density-dependent melanization than are larvae of other common clones (Fu-
tuyma et al. 1981). Melanization results in faster larval development and lower adult 
weight (Schneider 1979, Futuyma et al. 1981), and smaller females were less likely to obtain 
a mating in a preliminary laboratory experiment (Harshman 1982). Thus, a propensity to 
melanize may have resulted in lower mating success for clone 1(C). Similarly, attributes of 
H A R S H M A N  A N D  F U T U Y M A ,  A N N A L S  O F  T H E  E N T O M O L O G I C A L  S O C I E T Y  O F  A M E R I C A  7 8  (1 9 8 5 )  
6 
other asexual genotypes, such as relative time of adult eclosion (Mitter et al. 1979), may 
affect mating success in populations of the fall cankerworm. 
 
Acknowledgments – We express our appreciation to Richard Koehn for generously providing facil-
ities for electrophoresis. We also thank Jerry Hilbish for assistance in the field. This is Contribution 
No. 525 from the Program of Ecology and Evolution at the State University of New York at Stony 
Brook. This research was supported by grants from the National Science Foundation (BSR 8306000) 
and the Whitehall Foundation. 
 
Note 
1. Current address: Department of Genetics, University of California at Davis, Davis, CA 95616. 
 
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Variation in Population Sex Ratio and Mating Success of Asexual Lineages of \u3ci\u3eAlsophila pometaria\u3c/i\u3e (Lepidoptera: Geometridae)

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