Starks, P. T. 2001: Alternative reproductive tactics in the paper wasp Polistes dominulus with specific focus on the sit-and-wait tactic. — Ann. Zool. Fennici 38: 189–199.
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Ratnieks, F. L. W., Monnin, T. & Foster, K. R. 2001: Inclusive fitness theory: novel predictions and tests in eusocial Hymenoptera. — Ann. Zool. Fennici 38: 201–214.
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Kaitala, A. & Katvala, M. 2001: Sexual interactions and conspecific exploitation in an egg-carrying bug. — Ann. Zool. Fennici 38: 215–221.
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Kaitala, V. & Kaitala, A. 2001: Altruism, intraspecific parasitism and reciprocity: egg carrying in the golden egg bug. — Ann. Zool. Fennici 38: 223–228.
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Foster, K. R., Wenseleers, T. & Ratnieks, F. L. W. 2001: Spite: Hamilton’s unproven theory. — Ann. Zool. Fennici 38: 229–238.
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Nonacs, P. 2001: A life-history approach to group living and social contracts between individuals. — Ann. Zool. Fennici 38: 239–254.
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Tarpy, D. R. & Page, R. E. Jr. 2001: The curious promiscuity of queen honey bees (Apis mellifera): evolutionary and behavioral mechanisms. — Ann. Zool. Fennici 38: 255–265.
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Crozier, R. H. & Fjerdingstad, E. J. 2001: Polyandry in social Hymenoptera — disunity in diversity? — Ann. Zool. Fennici 38: 267–285.
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Daly, M. & Wilson, M. 2001: An assessment of some proposed exceptions to the phenomenon of nepotistic discrimination against stepchildren. — Ann. Zool. Fennici 38: 287–296.
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Basolo, A. L. 2001: The effect of intrasexual fitness differences on genotype frequency stability at Fisherian sex ratio equilibrium. — Ann. Zool. Fennici 38: 297–304.
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Galvani, A. P., Coleman, R. M. & Ferguson, N. M. 2001: Antigenic diversity and the selective value of sex in parasites. — Ann. Zool. Fennici 38: 305–314.
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Getz, W. M. 2001: Competition, extinction, and the sexuality of species. — Ann. Zool. Fennici 38: 315–330.
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Contents of Volume 38. — Ann. Zool. Fennici 38: 331.
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Starks, P. T. 2001: Alternative reproductive tactics in the paper wasp Polistes dominulus with specific focus on the sit-and-wait tactic. — Ann. Zool. Fennici 38: 189–199.

Polistes dominulus females that adopt nests are less cooperative and may expend less energy than nest founding wasps. In an enclosure, 14 nests were adopted by individuals previously unassociated with any nest. No preference for enclosure or non-enclosure nests was detected, suggesting that adopters do not preferentially secure nests containing non-descendent kin. Instead, adopters — who were significantly less likely cooperate than nest constructing wasps — maximized direct fitness benefits by adopting nests most likely to produce reproductives. Preliminary data comparing body weights of adopters to nest constructors suggests that, relative to nest constructors, adopters gain weight during the nest founding period. Combined, these results indicate that adopters are less cooperative than nest initiators, prefer mature nests to nests with a higher likelihood of kinship, and may conserve energy during the nest founding period. Several additional reproductive tactics were observed and a preliminary flow diagram of these options is provided.

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Ratnieks, F. L. W., Monnin, T. & Foster, K. R. 2001: Inclusive fitness theory: novel predictions and tests in eusocial Hymenoptera. — Ann. Zool. Fennici 38: 201–214.

Hamilton’s first papers concerned social evolution and revolutionized our understanding of reproductive conflict in insect societies. The revolution continues. Recent research at the University of Sheffield has investigated two topics previously not considered from an inclusive fitness perspective: dominance hierarchies and queen–worker caste conflict. The theory makes predictions close to that occurring in hierarchies of Dinoponera queenless ants and queen overproduction in Melipona bees. An earlier prediction, that multiple paternity favours worker policing, is supported by research on Vespula and Dolichovespula wasps. However, worker policing also occurs in the hornet, Vespa crabro, which has low paternity (effective queen mating 1.1). Worker policing in Vespinae wasps has two novel facultative features. In Dolichovespula saxonica, worker policing occurs in colonies headed by a multiple-mated queen but not by a single-mated queen. In Vespa crabro, queenless colonies accept worker-laid eggs but reject queen-laid eggs, probably because queen supersedure does not occur but queen parasitism does.

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Kaitala, A. & Katvala, M. 2001: Sexual interactions and conspecific exploitation in an egg-carrying bug. — Ann. Zool. Fennici 38: 215–221.

Female ability to exploit conspecifics may have unusual expressions. Golden egg bug (Phyllomorpha laciniata, Heteroptera, Coreidae) females lay eggs on the backs of conspecifics. Eggs are only attached on bugs and no active care is given. Egg carrying is costly due to increased predation risk. Females do not choose any particular “back” but lay eggs on all conspecifics available. Females carry one third of the eggs, and they never carry their own eggs. The majority of the eggs carried by males in the field are not fathered by the carrier. Females commonly dump eggs during reproductive activities on courting males or on (other) copulating females and males. In most habitats, eggs do not survive unless carried. Thus, females are dependent on the availability of conspecifics to lay eggs. Here, we review current knowledge on egg carrying and explore the costs of carrying eggs, how eggs are received and who carries the eggs. We also compare this system with that of arthropods which have exclusive paternal care. The main conclusion is that the system is a special form of intraspecific parasitism. It is maintained by high fitness benefits to an egg-dumping female and probably by rather low costs to an egg-carrying bug. Reproductive activities provide egg-laying opportunities for a female, and thus sexual interactions resulting from female polyandry are necessary for female egg dumping.

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Kaitala, V. & Kaitala, A. 2001: Altruism, intraspecific parasitism and reciprocity: egg carrying in the golden egg bug. — Ann. Zool. Fennici 38: 223–228.

The evolutionary theories of helping assume reciprocity, genetic relatedness or group selection. The evolution of an altruistic act, that is, a costly act by an individual that benefits another unrelated individual, often requires reciprocal interactions. Therefore, models of evolutionary stability (ESS) have been successful in studying the evolution of altruistic behavior. Nevertheless, altruistic behavior may evolve without reciprocity. Such a situation may arise when altruistic behavior is costly but other behavioral alternatives lead to more costly outcomes. However, this setting may closely resemble intraspecific parasitism where one individual exploits the resources, behavior or actions of another. Egg carrying behavior in the golden egg bug (Phyllomorpha laciniata Vill, Heteroptera, Coreidae) exemplifies the close and problematic relation between altruism and parasitism. The golden egg bug females lay eggs on the backs of female and male conspecifics. Egg carrying in the golden egg bug can be understood as intraspecific parasitism, altruistic behavior, reciprocity, or paternal care depending on which individual is receiving the eggs, from whom, and when. In this paper, we discuss the alternative theories in order to understand the unique reproductive behavior in the golden egg bug.

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Foster, K. R., Wenseleers, T. & Ratnieks, F. L. W. 2001: Spite: Hamilton’s unproven theory. — Ann. Zool. Fennici 38: 229–238.

Thirty years ago Hamilton showed that spite, an action that harms a recipient at no direct benefit to the actor, could evolve if interactants were negatively related. Wilson later showed that spite could also evolve by indirect benefits to a third party. Since then, many selfish actions that are particularly harmful to the recipient have been called ‘spite’ but no convincing examples have been found. Here we discuss three examples of spite from the social insects: worker policing, sex allocation biasing by workers and green beard queen killing in the fire ant. All examples are Wilsonian spite and the last example is also Hamiltonian spite. Spite will be harder to identify in other animals because actions that seem mutually harmful may have delayed reproductive benefits. Spite may prove to be more common at the genetic level than the individual level because negative relatedness can more easily arise. Two possible examples, cytoplasmic incompatibility and maternal-effect lethal distorter genes, are discussed.

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Nonacs, P. 2001: A life-history approach to group living and social contracts between individuals. — Ann. Zool. Fennici 38: 239–254.

A social behavior continuum from simple to complex is argued to be a basis for evolutionary categorization of species. I propose a complimentary view that compares similar life history decisions because social complexity varies in many species across their lifetimes. I specifically concentrate on the evolution of reproductive skew in cooperative breeding, which I define relative to the ability of group members to live solitarily or move easily between groups (i.e., facultative versus obligate eusociality). Facultative cooperation can arise through social contracts based either on conventions (arbitrary asymmetries determines status), or transactions (individuals cede benefits for group stability). These mechanisms predict different within-group dynamics. An analysis of transactional models predicts eusocial evolution requires large asymmetries between dominants and subordinates in ability to succeed independently. The only major exception appears to be cooperative colony initiation by polistine wasps. Their behavior, however, may have evolved due to a unique combination of reproductive gains through sex ratio conflicts with workers and factors that select for reproductive plasticity in offspring. Examining eusocial evolution as a specific life history trait also suggests that facultative versus obligate cooperation correlates with assumptions about dominant control over skew within groups. ‘Concession’ type models tend to predict behavior in facultative situations, while ‘Tug-of-war’ models do better in obligate situations.

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Tarpy, D. R. & Page, R. E. Jr. 2001: The curious promiscuity of queen honey bees (Apis mellifera): evolutionary and behavioral mechanisms. — Ann. Zool. Fennici 38: 255–265.

Even after considerable effort and debate, it remains unclear why honey bee queens frequently mate with 10 or more males. We address both why polyandry is adaptive to queens and how queens obtain such extreme numbers of mates. We review a manipulative experiment which tested the hypothesis that multiple mating reduces the genetic load caused by the honey bee sex determination system. Our results suggest that multiple mating (i.e., mating more than once) increases a queen’s fitness by lowering the probability that she produces a high proportion of inviable, diploid males within her brood. Furthermore, we examined the relationship between a queen’s mating behavior and her mating number. We propose that “extreme” polyandry in honey bees (i.e., mating numbers >= 10) may be inadvertent consequences of a queen’s mating behavior, therefore additional adaptive arguments are not needed to explain why honey bees have some of the highest mating numbers among the social insects.

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Crozier, R. H. & Fjerdingstad, E. J. 2001: Polyandry in social Hymenoptera — disunity in diversity? — Ann. Zool. Fennici 38: 267–285.

Multiple mating by queens occurs in many species of social Hymenoptera despite its likely costs. Hypotheses to explain multiple mating include a need for more sperm than provided by a single male, the convergence of queen and worker sex-allocation optima and various genetic diversity hypotheses. For some species the sperm need hypothesis fails since queens retain only a single male’s worth of sperm. In other cases, sperm store does increase with the number of matings. Similarly for the sex-allocation and genetic diversity hypotheses, data from some species are in support, those from others are not. Comparative analysis reveals a negative correlation between level of genetic diversity (of which queen mate number is an important determinant) and parasite load; findings in the best-studied case are complex: monandry and higher levels of polyandry are each selectively favored over moderate polyandry. Out of 14 identifiable hypotheses five are judged most useful for future work. Unfortunately, the search for a simple unitary model to explain all cases seems futile. A model encompassing all of these factors is desirable for studies on single species, but would be complex. Comparative analyses remain desirable, but should encompass the likelihood that different factors predominate in different groups.

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Daly, M. & Wilson, M. 2001: An assessment of some proposed exceptions to the phenomenon of nepotistic discrimination against stepchildren. — Ann. Zool. Fennici 38: 287–296.

Stepparents commit child abuse and homicide at much higher rates than genetic parents. Proposed exceptions, including a recent claim that there is no such “Cinderella effect” in Swedish homicides, are shown to be mistaken. The hypothesis that only “mothers’ boyfriends” abuse children excessively, whereas married stepfathers do not, is tested and rejected in an analysis of Canadian homicides. De facto marriage and steprelationship are confounded, but each is a major risk factor when the other is controlled. Abuse is a rare and presumably non-adaptive manifestation of discrimination, but recent research confirms that stepchildren are more generally disadvantaged with respect to positive investments. There are no known exceptions to the ubiquitous phenomenon of parents discriminating, on average, against stepchildren, but there is cross-national variation in the magnitude of these effects, and the determinants of this variability warrant investigation.

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Basolo, A. L. 2001: The effect of intrasexual fitness differences on genotype frequency stability at Fisherian sex ratio equilibrium. — Ann. Zool. Fennici 38: 297–304.

Fisherian sex ratio evolution is based on a set of common assumptions which, if met, will result in the maintenance of an equilibrium sex ratio of 0.5. One of these assumptions is the absence of intrasexual fitness differences. To investigate Fisherian sex ratio selection, variation is provided by three factor sex determination systems like that found in the platyfish, Xiphophorus maculatus. Here, populations with genetically-based intrasexual fitness differences were established at a sex ratio predicted to be at Fisherian equilibrium. The frequency of earlier versus later maturing genotypes changed in these populations, resulting in a sex ratio of 0.5, but at a different point along a curve of Fisherian sex ratio equilibria. Thus it appears that genetic differences in fitness which are in linkage with sex-determining factors can result in evolution along the sex ratio equilibrium curve.

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Galvani, A. P., Coleman, R. M. & Ferguson, N. M. 2001: Antigenic diversity and the selective value of sex in parasites. — Ann. Zool. Fennici 38: 305–314.

We employ a stochastic model of helminth transmission to explore the persistence properties of sexual versus asexual parasites in the face of a host population that develops immunity. We assume that this immunity is specific to the parasite strain, such that different parasite strains express unique antigens which in turn elicit specific host immune responses. Sexual parasites are inherently disadvantaged by a fecundity that is only half that of asexual parasites, given that males do not produce offspring. However, we demonstrate that sexual parasites benefit from the greater production and maintenance of antigenic genotypes than mutation alone in asexuals. The ability of sexual parasites to produce antigenic diversity enhances population persistence of the parasites, given that enhanced antigenic diversity permits evasion of host immunity. Therefore, we argue that sexual reproduction for parasites under intense negative frequency dependent selection induced by host immunity is associated with advantages that may be sufficient to compensate for lower intrinsic reproductive potential.

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Getz, W. M. 2001: Competition, extinction, and the sexuality of species. — Ann. Zool. Fennici 38: 315–330.

Considering the well-known two-fold cost of males associated with sexual reproduction, the maintenance of sex despite natural selection remains an enigma for population biologists. The prevalence of sex among eukaryotes is most commonly explained by hypotheses associated with either the purging of deleterious mutations, the generation of favorable gene combinations, the fixation of beneficial mutations, or, less frequently, ecological theories dealing with the coexistence of competing populations. Almost all these hypotheses ignore the fact that in stochastic environments, asexual populations exhibit higher rates of extinction than sexual populations because the latter generally exploit a wider spectrum of resources than their asexual counterparts. Here we develop a model to demonstrate, in populations where mutations from sexual to asexual reproduction are possible, that three reproductive phases — sexual, mixed, and asexual — naturally arise among competing sexual and asexual lines. The particular phase observed is related to the level of stochasticity in the environment experienced by the population complex in question (e.g. a partially competing group of congeneric species) and is a manifestation of the tension that exists between the reproductive superiority of asexual populations and their higher rates of extinction. I term this explanation the demographic balance hypothesis and suggest the endeostigmatid mites provide a suitable taxon for testing this hypothesis.

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