mals. Specifically, a phylogeny allows one to determine
whether a behavior is the result of shared common ancestry
or evolved independently in response to similar environ-
mental conditions. For instance, behavioral or ecological
traits that enhance the fitness of individuals under specific
environmental conditions can become established in popu-
lations, and if species occupying similar niches and envi-
ronments experience similar selective pressures, one might
expect evidence of convergence with respect to those traits.
A phylogeny allows one to map traits and directly test for
evidence of convergent evolution. Phylogenies also allow for
tracing combinations of behavioral traits that may or may
not map to the same node of the tree. In short, a phyloge-
netic perspective allows one to evaluate the function of a
particular behavior as well as the evolution of that behavior.
There is a presumption that current environmental fac-
tors provide an explanation for the evolution of life-history
traits associated with behavioral and ecological strategies
(e.g., Dobson and Oli, chap. 8, and Kalcounis-Rüppell and
Ribble, chap. 6, this volume). For instance, it has been hy-
pothesized that the formation of complex social groups
reflects a compromise between the cost of dispersal versus
the cost of foregoing reproduction and staying within the
natal group (e.g., Nunes, chap. 13 and Solomon and Keane,
chap. 4, this volume). In similar environmental circum-
stances defined by limited food resources, risk of predation,
and lack of suitable territory, short-term costs associated
with alloparenting and other forms of reproductive altru-
ism are offset by long-term benefits of staying within the na-
tal group (Alexander 1974; Lacey and Sherman, chap. 21,
this volume). A phylogeny provides a means of testing such
predictions. In the following we provide two examples of
how this phylogenetic approach can be used.
Evolution of mating systems in cavioid rodents
The superfamily Cavioidea represents a monophyletic group
(Woods 1993; Nedbal et al. 1996; Huchon et al. 1999) of
South American hystricognath rodents that display a di-
verse array of behaviors, ecological specializations, and life-
history strategies. For instance, habitat use by members of
this superfamily ranges from generalists to desert special-
ists, with the habitat occupied by the former defined by an
even distribution of resources and the latter by clumped re-
sources. Mating systems in cavioid rodents are also diverse,
ranging from hierarchical promiscuity to polygyny and mo-
nogamy (Kleiman et al. 1979; Macdonald et al., chap 33,
this volume). In view of differences in habitat use and mat-
ing systems observed with the Cavioidea, Lacher (1981)
proposed the ecological constraints hypothesis. This hy-
pothesis relied on the classical taxonomy of the Cavioidea,
which divides members of the family Caviidae into two sub-
families, Caviinae and Dolichotinae. Except for Kerodon
rupestris(rock cavy), which displays a polygynous mating
system and the formation of social groups, most members
of the Caviinae, such as Cavia apera(common guinea pig),
Galea musteloides,and Microcavia australisdisplay hier-
archical promiscuity and low levels of sociality. Members
of the Dolichotinae, Dolichotis patagonumand Pediolagus
salinicola,are socially complex and have a monogamous
mating system. Given the presumed phylogenetic placement
ofKerodon rupestris,Lacher (1981) suggested that the com-
plex social system and mating system seen in Kerodoncon-
verged on that seen in the Dolichotinae, primarily in re-
sponse to similar ecological constraints related to increased
risk of predation and the distribution of resources. Rowe
and Honeycutt (2002) used nucleotide sequences from both
nuclear and mitochondrial genes to derive a molecular phy-
logeny for the Cavioidea. This phylogeny was used to test
Lacher’s (1981) original hypothesis and to examine the cor-
relation between character evolution and characteristics
of both habitat and degree of sociality. The molecular phy-
logeny (fig. 2.7) did not support current ideas of cavioid
taxonomy, placing Kerodon,the capybara (Hydrochaeris
hydrochaeris), and members of the Dolichotinae in a mono-
phyletic clade characterized by increased sociality and com-
plex mating systems. In fact, there was strong support for
a sister-group relationship between Kerodonand Hydro-
chaeris,both of which are habitat specialists and have a
harem-based mating system. A concentrated-changes test
(MacClade 3.1; Maddison and Maddison 1992) suggested
that the probability of sociality and habitat specialization
being associated by chance alone was high. Therefore, the
ancestor of this clade may have been social, thus allowing
for the occupation of habitats characterized by patchily dis-
tributed resources and /or increased predation. This study
should be expanded to include more diversity within the
hystricognaths in general.Life-history traits and social complexity
Blumstein and Armitage (1998a) devised a metric for de-
gree of social complexity and used independent contrasts
analysis to evaluate the consequences of social complexity
in terms of the evolution of life-history traits (e.g., number
of breeding females, time to first reproduction by females,
gestation time, litter size, and survival of first offspring). Us-
ing current taxonomy as the phylogenetic framework, the
following results were obtained: (1) an increase in social
complexity results in fewer breeding adult females and
higher survival of first-year offspring; (2) there is a corre-
lation between age at first breeding and social complexity,20 Chapter Two