A
s you are undoubtedly aware by now,
Rodent Societiesis unabashedly a work of enlight-
ened natural history — that is, authors have pre-
sented details of the natural behavior, physiology, and so-
cial ecology of various rodents and have then interpreted the
facts in light of modern evolutionary theory. Every chapter
has proudly and enthusiastically highlighted new results and
synthesized existing information about the sociobiology of
one or more rodent species (much of which was scattered
hitherto), and has then analyzed the results through devel-
oping and testing alternative hypotheses at one or more of
the four levels of analysis: mechanisms, ontogenies, fitness
consequences, or evolutionary histories.
Every chapter in Rodent Societiesconcludes with a brief
summary. Perusal of these summaries indicates how much
we presently know about that topic. On the one hand, the
amount of information is impressive, especially about cer-
tain subjects and taxa. On the other hand, it is obvious that
a tremendous amount of information remains to be discov-
ered. This is hardly surprising, since long-term studies of be-
havior and ecology have been conducted on less than 10%
of the more than 2,000 species of rodents. At this rate, many
species probably will go extinct without ever having been
studied in detail! Even in well-studied species, we know
very little about intraspecific (interpopulation) variations
— for example, in annual cycles, digestive and hibernation
physiology, demography, food preferences, mating systems,
and social behavior. In no rodent species has any social
or reproductive behavior been completely elucidated at all
four levels of analysis.
Various authors infer from observing the behavior of
their study animals that rodents are making complex cost /
benefit decisions about how to behave so as to maximize
fitness. However, actual measurement of fitness differences
among behavioral variants is rare, and no one understands
the physiological, genetic, or ontogenetic mechanisms un-
derlying adaptive decision making. Similarly, theory about
the functions of facultative sex ratio adjustment is mature,
but the extent of the predicted adjustments at conception
and their underlying physiological and ontogenetic mech-
anisms are unknown. Neophobia and neophilia are well
documented in some rodents, but their mechanisms, onto-
genies, and evolutionary histories are essentially unstudied.
And despite the current revolution in molecular biology,
we know very little about the genetic and ontogenetic bases,
or the evolutionary histories of variations in life histories,
sex ratios, and developmental programs, nor social behav-
iors such as kin recognition, alloparental care, dispersal, or
alarm calling.
Even regarding fitness consequences — the level of anal-
ysis at which we and most other behavioral ecologists
work— many intriguing and important questions about ro-
dent sociobiology remain. For example, no one has quan-
tified the fitness consequences of recognizing or not recog-
nizing kin, giving or not giving an alarm call, or committing
or not committing infanticide. Alternative reproductive tac-
tics, infanticide, and natal dispersal are widespread in
rodents, and multiple hypotheses have been proposed to ex-
plain the adaptive significance of each phenomenon. How-
ever, few of these hypotheses have been adequately tested in
nature for even a single species — that is, using the strong-
inference approach and manipulative experimentation. A