Article
Regional Variation in Sex Ratios and Sex Allocation in Androdioecious Mercurialis annua
Journal of Evolutionary Biology
(2014)
Abstract
In androdioecious metapopulations, where males co-occur with herma-
phrodites, the absence of males from certain populations or regions may
be explained by locally high selfing rates, high hermaphrodite outcross sir-
ing success (e.g. due to high pollen production by hermaphrodites), or to
stochastic processes (e.g. the failure of males to invade populations or
regions following colonization or range expansion by hermaphrodites). In
the Iberian Peninsula and Morocco, the presence of males with hermaph-
rodites in the wind-pollinated androdioecious plant Mercurialis annua (Eu-
phorbiaceae) varies both among populations within relatively small regions
and among regions, with some regions lacking males from all populations.
The species is known to have expanded its range into the Iberian Penin-
sula from a southern refugium. To account for variation in male presence
in M. annua, we test the following hypotheses: (1) that males are absent
in areas where plant densities are lower, because selfing rates should be
correspondingly higher; (2) that males are absent in areas where her-
maphrodites produce more pollen; and (3) that males are absent in areas
where there is an elevated proportion of populations in which plant den-
sity and hermaphrodite pollen production disfavour their invasion. We
found support for predictions two and three in Morocco (the putative
Pleistocene refugium for M. annua) but no support for any hypothesis in
Iberia (the expanded range). Our results are partially consistent with a
hypothesis of sex-allocation equilibrium for populations in Morocco; in
Iberia, the absence of males from large geographical regions is more con-
sistent with a model of sex-ratio evolution in a metapopulation with
recurrent population turnover. Our study points to the role of both fre-
quency-dependent selection and contingencies imposed by colonization
during range expansions and in metapopulations.
Disciplines
Publication Date
July, 2014
DOI
10.1111/jeb.12352
Citation Information
J. R. Pannell, S. M. Eppley, M. E. Dorken & R. Berjano. (2014). Regional Variation in Sex Ratios and Sex Allocation in Androdioecious Mercurialis annua. Journal of Evolutionary Biology, 27(7), 1287-1499.