1. The increase of
variance in male
reproductive success
by extra-pair paternity
(EPP)
Félix Vallés
University of Puerto Rico –Cayey
Biology Department
to the variation in overall male reproductive
success. Hence, EPC increases the potential
for sexual selection. Investigation of EPP in
zebra finchesin the Australian desert
revealed that 1.7% of 316 offspring from
four of 80 broods were fathered outside the
pair bond. These numbers imply a low level
of sperm competition and sexual selection in
natural populations. EPP in the wild zebra
finch has vital suggestions for future studies
of sexual selection and reproductive biology.
By studying these socially monogamous
birds, the purpose of EPP and how it
increases the variation in male reproductive
success, should be better understood.
RISE Program
INTRODUCTION
Biol. 3095 Seminar Scientific Literature and
Bibliography
ABSTRACT
Seabirds are usually exposed to sperm
competition due to potential and possessive
mating partners and colonial breeding.
Nevertheless, paternity studies usually
reveal low rates of extra-pair paternity (EPP)
in colonial seabirds. Investigation of extrapair (EP) and within-pair (WP) copulation
endeavors of the little aukrevealed that more
than 60% engaged in EP copulation (EPC)
and only 2% (8/330) of all copulations were
successful, which significantly alters the
reproductive success among males in
monogamous species. Ornamental traits
evolve if they furnish individuals with an
advantage in ensuring multiple mates. EPP
is common in the mountain bluebird with
72% of broods containing at least one EP
offspring. WP and EP offspring contributed
Many socially monogamous birds, which
tend to have a single mating partner during
most of their life, participate in sexual
relations with other mates besides their life
partner. This affair is called extra-pair
copulation (EPC) and can lead to offspring.
The fathering of the offspring by the extrapair (EP) male bird is known as extra-pair
paternity (EPP). The purpose of this paper is
to compare the phenomenon of EPP between
the mountain blue bird (Sialiacurrucoides),
the little auk (Allealle) and the zebra finch
(Taeniopygiaguttata) for a better
understanding its purpose and how it
increases the variation in male reproductive
success.

2. MATING PATERNS
MOUNTAIN BLUEBIRD(Sialiacurrucoides)
The mountain bluebird(Sialiacurrucoides) is
a socially monogamous songbird with
striking male plumage ornamentation (an
attractive feature or structure that serves to
entice mates). The exhibition of this trait is
an advantage to males since it guarantees
multiple mates.According to the good genes
hypothesis (Fisher, 1958), extra pair
offspring (EPO) of the EP mate presenting
this trait should have better life conditions
than within pair offspring (WPO) and hence
assuring the future reproduction of the
offspring.
LITTLE AUK
(Allealle)
The little auk (Allealle)is a typical seabird
with a socially monogamous breeding
system.Given that the little auk is a colonial
breeder, meaning that within-pair
copulations (WPC) take place regularly,
EPC occurs frequently but is unsuccessful;
hence EPP take place at low rate. Another
explanation for the low rates of EPP is that
females can efficiently resist fertilization by
EP males.
For mating, male little auks use postures and
vocalizations to attract females. If a male is
found suitable, the female will engage in a
‘head bowing’ ceremony that involves
facing each other and bowing their heads.
Then, ‘clucking’, bill touching, and
fluttering of wings occurs. Pairs then engage
in a ‘Butterfly’ flight, ritualized walks or
unique displays of postures. After this,
copulation occurs. (Freethy, 1987; Gaston
and Jones, 1998; Harris and Birkhead, 1985;
Sibley, 2001)
ZEBRA FINCHES
(Taeniopygiaguttata)
Zebra finches (Taeniopygiaguttata) have a
high capacity to breed, even in the most
unfavorable conditions. This bird has
become one of the most used model
organisms for the study of sperm
competition and sexual selection.Sperm
competition in birds occurs when multiple
potential mating partners inseminate a
female during a single breeding cycle and
can result in EPP. This event is related to
sexual selection since the outcome of male
reproductive success is different. In sexual
selection,some traits such as plumage, song
and behavior are directly related to female
selection and therefore mating success.
Zebra finches present some traits or
characteristics that favor their sexual
selection such as parental care (Burley
1988), in which parental personality traits
have positive effects in offspring fitness.
These non-genetic parental effects are
carried over into the next generation; hence
thesebehavioral traits of biparental species
can have important, long-lasting effects on
reproductive success. Another characteristic
that favors female selection is sex allocation
(Burley 1981), in which parents should
prefer the investment towards offspring of
the sex that grants higher relative fitness on
the parent. Maternal effects (Gil et al. 1999)
are another trait present in female zebra
finches which occur when offspring
phenotype is affected by environmental
factors experienced by the mother.
Mothersinvest in certain offspring in ways

3. that will maximize their fitness according to
the offspring’s independency.
VARIATION IN MALE REPRODUCTIVE
SUCCESS
According to(Balenger 2009)EPC greatly
increases male reproductive success in the
studied population. Nevertheless, the results
may not be so precise due to the exclusion
of several males and nestlings and the use of
artificial nest boxes, which may have led to
miscalculations. Another factor that
influenced the findings is the elimination of
some settled males that were unsuccessful in
WP reproduction. Furthermore, the analyses
do not include second breeding endeavors.
Moreover it is not known whether males that
have high or low WP and/or EP
reproductive success during first breeding
attempts tend to be involved in second
breeding attempts. Nor is it known how the
paternity in second attempts differs from
those in first attempts (Kleven et al. 2006).
(Wojczulanis-Jakubas 2008)suggests that
(94%) of EPC in little auks were
unsuccessful and therefore only 2% (8/330)
were successful. These numbers are precise
because the analyses were based on 64
families. It also states that by engaging in
EPC, females ensure against their mate’s
infertility. Due to the high rates of WPC,
females swamp the sperm from EP males for
the sperm of their mate.
Griffith and collaborators in 2010 compared
the levels of EPP between wild zebra
finches located in the Australian desert and
captive North American domestic zebra
finches in a single aviary. There were very
low levels of EPP in the desert (1.7%
offspring in 5% of broods) whereas in the
aviary 28% of 278 offspring in 37% of 126
broods were fathered by an EP sire,
indicating very high rates of EPP. Artificial
selection imposed by aviculturists or the
social or environmental factors may be the
cause for the difference in EPP rates
between these environmental conditions.
Studies propose that the main causes of
variation in EPP levels are breeding density,
breeding synchrony, habitat complexity,
paternal care, adult mortality, food
availability, and genetic diversity. The
density hypothesis (Brikhead 1978) states
that the greater the density of a population,
the grater the opportunity of males
participating in EPC will be given that the
distance between them is smaller and there
is greater abundance of females. Stutchbury
and Mortin’s (1995) hypothesis propose that
synchronious breeding endorses EPC
because it provides better accessibility of
male quality to females. The availability of
food influencesEPP by influencing the need
for paternal care or affecting the population
density.
CONCLUSION
EPP greatly varies among species due to
their contrast in behavior, sexual selection
and life style. Male mountain bluebirds
presenting plumage ornamentation that
participate in EPP do increase the variance
for reproductive success for its progeny if
the sired offspring(s) is/are also male(s).
Other than the postures, ceremonies and
flights, which are learned, used by little auks

4. to entice mates, vocalizations are the only
traits that are genetic and therefore can also
increase male reproductive success.
Similarly, all the traits presented by the
zebra finch to attract mates are non-genetic
except for ornamental song, which should
also increase male reproductive success.
CITED LITERATURE
Balenger SL, Johnson LS, Mays HL Jr.,
Masters BS. 2009. Extra-Pair Paternity in
the Socially Monogamous Mountain
Bluebird Sialiacurrucoides and its Effect on
the Potential for Sexual Selection. Journal of
Avian Biology 40(2): 173-180.
Griffitha SC, Holleleya CE, Mariettea MM,
Prykea SR, Svedina N. 2010.Low level of
extrapair parentage in wild zebra finches.
Animal Behaviour Volume 79, Issue 2 p
261–264
Hoi H,Griggio M.2010. Monogamy and
Extra-Pair Parentage.Encyclopedia of
Animal Behavior.p 475–482
Wan D, Chang P, Yin J. 2013.Causes of
extra-pair paternity and its inter-specific
variation in socially monogamous
birds.ActaEcologicaSinica Volume 33, Issue
3, p 158–166
Wojczulanis-Jakubas K, Jakubas D,
Øigarden T,Lifjeld JT. 2008. Extrapair
copulations are frequent but unsuccessful in
a highly colonial seabird, the little auk,
Allealle. Animal Behaviour: 1-6