Are Pinyon Jays Gymnorhinus cyanocephalus Genetically Monogamous

1
Are Pinyon Jays (Gymnorhinus cyanocephalus)
Genetically Monogamous?
Barber, M., Benford, R., and Balda, R.P.
Avian Cognition Laboratory Department of
Biological Sciences Northern Arizona University
Flagstaff, AZ 86011

Methods
Discussion
Abstract
Results from this experiment suggest that pinyon
jays do not perform extra pair copulations. Data
on social parentage were consistent with data on
genetic parentage in each of the examples
considered. The finding that pinyon jays are
genetically monogamous seems to justify the high
level of parental investment that both males and
females make in their offspring. While this
research provided useful information on the
reproductive fidelity of male pinyon jays, the
findings must be interpreted cautiously. Pinyon
jays in the study were captive, and their options
for choosing both social and reproductive
partners were restricted. In the wild, the
opportunity for extra pair copulations may be
increased because females have a broader range of
possible mates and potential accomplices in
cuckoldry. Furthermore, the sample size in this
study is prohibitively small. More breeding
events that yield more complete genetic
information should be considered before a strong
conclusion can be made. Future research should
include a larger number of adults, breeding
permutations, and eggs. Techniques should be
improved to provide more valid genetic data at
more loci. Finally, genetic data from wild birds
should be used to more accurately characterize
the mating dynamics of this species.
To describe the social relationships within a
flock of 22 wild-caught, captive pinyon jays,
behavioral observations were performed in an
outdoor aviary at the outset of each of the
2003-05 breeding seasons. Birds were observed in
three minute intervals for four hours daily, for
a one week period before nest-building began.
Observation schedules were randomized, such that
birds were observed in different sequences in the
morning, mid-day, and afternoon. Data on
courtship, neutral, and agonistic behaviors,
described by Marzluff and Balda 1992, among dyads
were collected. Dyads with the greatest number
of courtship and the fewest number of agonistic
interactions were categorized as social partners.

Pinyon jays are socially monogamous and form
lifetime pair bonds. Both females and males
invest heavily in parental care. The likelihood
that social parents are genetic parents is high,
but the level of genetic monogamy in this species
is unknown. To determine the rates of monogamy
and extra pair paternity, observations were made
to identify the social relationships of 22 (11
female and 11 male) captive adult pinyon jays in
a single flock. Birds were then paired with
their social partners, with individuals that were
not their social partners, and in small groups
that contained their social partners and other
individuals. Birds were given the opportunity to
breed. DNA was collected from parental birds
(n22) and all embryos (n 24) produced. Allele
frequencies were compared at 6 VNTR loci.
Exclusion analyses were performed to establish a
list of putative parents for each embryo.
Relatedness was calculated for each hypothesized
parent-offspring dyad, and a list of most likely
parent-offspring triads was derived. Genetic
triads were compared to observational data on
adult pair-bonding. In each case, social triads
matched genetic triads. These data support the
hypothesis that pinyon jays are genetically
monogamous, and suggest that a high level of
parental investment from both sexes is justified.
For the three breeding seasons in the study,
females were placed in experimental conditions
where they were given the opportunity to breed
with their social partner, with other males in a
group containing their social partner, and with
males in a group that did not contain their
social partner. Eggs that were produced were
collected. DNA was extracted from each viable
embryo. Genetic information from six VNTR loci
was obtained for all embryos and adult birds in
the study. An exclusion analysis was performed
to establish a list of putative parents for each
embryo. Relatedness of each parent-offspring dyad
was also calculated (Queller and Goodnight 1989).
From the list of putative parents, the adult male
and female that had the highest relatedness
values were classified as the embryos genetic
parents. Genetic paternity was compared to
observational data on social partnerships.
Introduction
References
Lack (1967) reported that 93 of passerine
species are normally monogamous. However,
since molecular techniques have allowed
researchers to determine true parentage, only 11
of passerine species have been demonstrated to be
genetically monogamous. Genetic monogamy, even
in socially monogamous species, seems to be the
exception rather than the rule. Pinyon jays are
socially monogamous and form life long pair
bonds. Both male and female pinyon jays invest
heavily in their offspring (Marzluff and Balda,
1992). A heavy male investment would provide a
direct payoff in fitness if his paternity were
assured. But if the males paternity were not
assured, he could be the victim of cuckoldry, and
the evolutionary return on his investment could
be diminished. This study is an attempt to
determine whether or not pinyon jays are
genetically monogamous.
Proximity
Table 2 (Below). Parentage data derived from
genetic analyses. Putative Parents are adults
that survive exclusion analysis. Relatedness
is genetic similarity of adult to embryo. 1.0
exactly similar, 0.0 as similar as one would
expect by chance by selecting two individuals
randomly from the flock, -1.0 as dissimilar as
possible considering allele frequencies present
in population.
Table 1 (Right). Number of eggs produced in each
experimental condition. Courtship condition 2
strong, 1 weak, 0 none. Proximity condition 2
same aviary, 1 adjacent aviaries, 0
non-adjacent aviaries. Shaded areas represent
conditions that would imply extra pair paternity.
Non-shaded areas represent conditions that imply
monogamy.
Lack, D.L. 1967. The Natural Regulation of Animal
Numbers, Oxford Clarendon Press. Marzluff, J.,
Balda, R.P. 1992. The Pinyon Jay Behavioral
Ecology of a Colonial and Cooperative Corvid.
London T A D Poyser. Queller, D.C.,
Goodnight, K.F. 1989. Estimating relatedness
using genetic markers. Evolution, 43, 258-275
Courtship
Acknowledgements
This work was funded by grant IBN 9882883 from
the National Science Foundation, and Northern
Arizona University. The opinions and conclusions
in this study are those of the study authors, and
are not necessarily shared by the National
Science Foundation or Northern Arizona
University. We thank Northern Arizona
Universitys College of Engineering and Natural
Sciences and the Department of Biological
Sciences for their support of and ongoing
commitment to undergraduate education and
research. We would also like to express our
gratitude to the Keim Genetics Laboratory for the
use of its facilities and helpfulness of its
staff, including Paul Keim, Talima Pearson,
Joseph Busch, and Sergey Kachur. We would like to
acknowledge Bryce Marshall and Kate Behn for
their sustained efforts in the field, and
Christian Nunes and Erin Strasser for their help
with data management and analysis.
Results
Of the 24 eggs produced, 15 yielded genetic data.
Parentage could be accurately determined for 9
of these eggs. In all 9 cases, genetic parentage
matched social parentage. Genetic data from 6
parent-offspring triads were incomplete and
yielded inconclusive results. All reproductively
active females (n6) produced eggs with only one
male. In each case, the female produced eggs
with the male that was identified as her social
partner. Table 2 (above) presents parentage data
for all viable embryos.
Figure 1. A clutch of pinyon jay eggs in the
nest. Pinyon jays normally have clutch sizes of
3-5 eggs. Pinyon jays begin breeding in January
and can lay multiple clutches per year (Marzluff
and Balda, 1992).
Figure 2. Pinyon jays engage in a variety of
courtship behaviors (Marzluff and Balda, 1992).
Here, a male pinyon jay takes a break from
allopreening his mate.