1384 NOTES AND COMMENTS Evolution, 39(6), 1985, pp. 1384-1388 THE USE OF PHYLOGENY IN BEHAVIOR AND ECOLOGY F. STEPHEN DOBSON Museum ofZoology and Division ofBiological Sciences University ofMichigan, Ann Arbor, MI48109 Received July 13, 1984. Accepted July 12, 1985 The comparativeanalysis ofcharacteristicsofdif­ characteristics are examinedfor correlationsamong ferent species is extensively used in evaluating pos­ themselves, or for correlations among characteris­ sible selective contexts for behavioral and ecolog­ tics and environments. Ifa group that shares a char­ ical differences among species (e.g., Alexander et acteristic is also a monophyletic group, then there al., 1979; Blumer, 1979; Bradbury, 1981; Dobson, is an alternative to explanations ofnatural selection 1982; Greenwood, 1980;Ralls, 1976;Steams, 1977; in recent (modem) environments: the characteristic Wittenberger, 1976;WittenbergerandTilson, 1980). might have evolved in a past environment, and it Such analyses often explicitly or implicitly assume is retained because superior alternatives did not that when species resemble each other in some be­ arise in the taxa. In an interspecific comparison in havioral or morphological characteristic, the re­ which monophyletic and character trait groups co­ semblance is due to independent appearance ofthe occur, the a priori historical origin hypothesis is an characteristic under study in each species in the equally valid hypothesis compared to any expla­ analysis. This assumption can be (but rarely is)tested nation of superior function (i.e., superior adaptive­ by examining evidence for independent evolution ness) in recent environments. of characteristics, deduced from a well supported Shared morphological characteristics in a mono­ hypothesis of phylogeny. In this essay, I will explain phyletic group are commonly thought to be influ­ how non-systematists in general, and behaviorists enced strongly by a commonancestry. For example, and ecologists in particular, can benefit from con­ numerous characteristics of reproductive mor­ sidering historical influences on the evolution of phology ofmarsupial mammals are shared widely characteristics. I will also indicate problems that within the clade (the monophyletic group), and they may be encountered in extracting a well supported are probably descended from a single ancestor and phylogeny from the systematic literature. conserved over evolutionary time (Lillegraven, 1974, 1975).Whether marsupial reproductive mor­ Historical Analysis phology is strongly constrained against change (Lil­ The characteristics that contemporary speciesex­ legraven, 1974, 1975) or highly adaptive in certain hibit may have evolved in their recent environ­ environments (Low, 1978), or both, it would be ment, or they may be of relatively older evolution­ unsatisfactory to explain the distribution ofrepro­ ary origin. That is, a group of related species may ductive characteristics between marsupial and pla­ have derived characteristics independently or from cental mammals solely as the result of natural se­ a common ancestor. Ifa characteristic is obtained lection operating in recent environments. The through descent from an ancestor, then in com­ historical origin hypothesis is corroborated by phy­ parison with the ancestor the characteristic may be logenetic analysis in this case, and it should be con­ ofgreater, equal, or less utility to individuals in the sidered a valid alternative to adaptive explanations. descendent species in coping with their respective The hypothesis of shared similarity due to shared contemporary environments. Genes for the char­ history can also be applied to behavioral studies. acteristic should remain in the genomes until a more For example, Greenwood (1980) found that char­ beneficialalternative characteristic arises. In a group acteristics of juvenile dispersal, with several im­ of contemporary species that share a particular portant exceptions, differed between birds and characteristic, therefore, it might be difficult to as­ mammals. In about 90% of bird species, juvenile certain just how beneficial the characteristic is in males and females disperse equally, or juvenile fe­ the respective environments ofthe species. Itmight males exhibit somewhat greater dispersal than ju­ be even more difficult (or impossible) to judge venile males. In about 70% of mammal species, whether alternative characteristics that have never males are the predominant dispersing sex among evolved in the group ofspecies might be more ben­ juveniles. The hypothesis that the characteristics of eficialthan an existing characteristic. Thus, it might these taxa might be shared among species because be misleading to assume that a characteristic is an they share a common historical origin should be adaptation to contemporary environments, and a considered along with the adaptive hypotheses dis­ characteristic that descends from a common ances­ cussed by Greenwood (1980). tor to contemporary species cannot be assumed to The historical origin hypothesis might also prove be of "optimal" benefit to individuals. illuminatingin population ecology.One of the most In interspecific comparisons, sets of alternative intensively studied questions in population ecology NOTES AND COMMENTS 1385 is why many species of microtine rodents exhibit hypotheses that invoke adaptation to recent envi­ "cyclic" or erratic outbreaks in population sizeevery ronments. three to four years. Krebs and Myers (1974) argued A second method can be used to insure that pat­ that the widespread occurrence of fluctuating mi­ terns of characteristics among taxa are likely to be crotine populations makes it likely that a single due primarily to historical origin. Alexander et al. causal mechanism is responsible. Perhaps a pro­ (1979) examined the degree of polygyny and degree pensity for cyclic fluctuations due to characteristics of sexual dimorphism in three distantly related taxa of individual microtine rodents (in particular en­ (pinnipeds, primates, and ungulates). Each taxon vironments) has been inherited by many microtine contained a wide range of variation in the charac­ speciesfrom their commonancestor. Ecologistshave teristics of polygyny and sexual dimorphism, and recently emphasized causal mechanisms that are the range of variation likely evolved independently "intrinsic" to fluctuatingmicrotine rodents, and they at least three times. While a consideration of his­ have assumed thatthe characteristics of individuals torical influences was not explicitly mentioned by that result in changes in population size are adap­ Alexander et aI. (1979), a primary influence of his­ tive in contemporary environments (e.g., Krebs, torical origin on the pattern of characteristics that 1978; Lidicker, 1978). An influence of historical they examined is unlikely. origin (an intrinsic factor) has not previously been Ridley (1983) suggested a third method for iden­ suggested. tifying independent evolution that assigns charac­ I will not present examples of the relevance of teristics to ancestors by successive "outgroup" the historical origin hypothesis to the study offunc­ comparisons. Such inference of behavioral or eco­ tional morphology, life history, or coevolution. logical characteristics of ancestors, however, is not Lauder (1981, 1982) presented methods for testing required for testing hypotheses of historical origin. the hypothesis of historical influence on morpho­ As the previous two methods indicate, all that is logicalform and argued that functional morphology required is evidence of the minimum number of should be viewed as an historical discipline. Steams independent evolutionary events (i.e., assignment (1983, 1984) has indicated a strong influence of of a hypothetical ancestral condition that minimiz­ phylogeny on the evolution oflife histories (but see es potential characterevolution). For example, Rid­ Vitt and Seigel, 1985), and the influence ofhistor­ ley (1983) states that his method cannot be used in ical origin was applied to the evolution of ecological cases like the study by Alexander et aI. (1979), de­ associationsby Mitter and Brooks(1983)and Brooks spite considerable evidence of independent evolu­ (1985). These studies indicate a growing interest in tion. the value ofconsidering the influence ofhistory in A fourth method that corrects comparative stud­ interspecific studies. Tests of historical influences ies for phylogeny was developed by Felsenstein need to be extended to studies of the evolution of (1985). This statistical methodology has consider­ behaviors and to additional subfields of ecology. able barriers to practical application (discussed by Such tests can be used as an important first step in Felsenstein), but it illustrates the difficulties in­ the design of research, in which groups of species volved in trying to separate environmental and his­ that are most likely to exhibit adaptations to recent torical influences on the characteristics of organ­ environments are chosen for testing evolutionary isms. Until methods for partitioning these influences hypotheses. are available, methods that indicate when the in­ The historical origin hypothesis can be tested by fluence of history is minimized or maximized will comparing the distribution of behavioral or eco­ likely be most helpful to behaviorists, ecologists, logical characteristics among species to a well sup­ and other functional biologists. ported phylogeny for the species. Ifthe distribution ofcharacteristicsamong species is inconsistent with Example the