Spatial analysis of morphological variation in African honeybees (Apis mellifera L.) on a continental scale
Apidologie
Spatial analysis of morphological variation in African honeybees (Apis mellifera L.) on a continental scale
José A.F. DINIZ-FILHO 3
H. Randall HEPBURN 1
Sarah RADLOFF 2
Stefan FUCHS 0
0 Institut für Bienenkunde (Polytechnische Gesellschaft), Fachbereich Biologie der J-W. Goethe Universität Frankfurt am Main , Karl-von-Frisch Weg 2, D-61440 Oberursel , Germany
1 Department of Zoology and Entomology, Rhodes University , P.O. Box 94, 6140 Grahamstown , South Africa
2 Department of Statistics, Rhodes University , P.O. Box 94, 6140 Grahamstown , South Africa
3 Departmento de Biologia Geral, ICB, Universidade Federal de Goiás , C.P. 131, 74.001-970 Goiânia, GO , Brazil
- Population differentiation of African honeybees has been analysed in a spatial context encompassing the continent's wide geographical range and environmental heterogeneity, based on 10 morphological characters measured from 268 local populations. While autocorrelation indicates a continuous large-scale decrease in similarity in general, clustering of single character correlograms suggests four distinct groups of profiles. This pattern, further supported by mapping factor scores, canonical trend surface analysis axes scores, suggests a variety of microevolutionary mechanisms acting at distinct scales in time and space in different groups of characters. Association with largescale differences in vegetation, climate and traditional subspecific classification has been analysed by analysis of variance (ANOVA). The most important aspect is that the results support the hypothesis that traditional subspecies, at least as defined by these characters, seem to represent integrated evolutionary units well adapted to their local conditions.
1. INTRODUCTION
During the last 30 years, different
multivariate statistical methods have been used
to analyse honeybee populations worldwide
[
20
]. In a generic sense, these methods have
been used to visualise the relative position of
observations (usually colony means) in a
dimensional reduced space, defined by
linear combinations of original morphometric
characters. In most situations, the purpose is
to test differences among a priori defined
groups, especially subspecies [
12, 20
].
In recent years, it has been recognised
that morphological and genetic variation
among honeybee populations should also
be investigated in a spatial context. There
are many advantages to this approach.
Firstly, since the microevolutionary
processes related to population differentiation
such as selection, migration and drift occur
in a spatial context, it would be easier to
infer these processes by analysing
morphometric variation in geographic space.
Secondly, since these processes usually
produce at least partially continuous variation,
the traditional approach of using
discriminant analysis to test differences among
subspecies is usually biased by the spatially
structured differences within these groups
[
5, 12, 18
].
Two different approaches have been used
to evaluate spatial variation in honeybees.
The easier of these is to extend the
traditional multivariate approaches, but
showing their results in a geographic context by
mapping and generating interpolated
functions from scores derived from factor,
principal component (PCA) or discriminant
analyses [2]. In this case, samples are also
taken in a spatial design, usually transects
[
13
]. On the other hand, direct spatial
analyses can also be performed, by pairing
geographic coordinates (latitude and longitude)
with mean vectors of local populations.
Trend surface and spatial autocorrelation
analyses have been used in these cases to
assess population structure and attempt to
make inferences about microevolutionary
processes involved in population
differentiation [3, 4, 6, 7].
Investigations about the population dif
ferentiation of African honeybees have been
traditionally carried out by partitioning
populations into different subspecies, since the
findings of Kerr and Portugal-Araújo [
15
].
After the introduction of multivariate
analyses into honeybee systematics, several
different typologies have been proposed [
12,
20
]. Because of the wide geographical range
and environmental heterogeneity
throughout the continent, differentiation among
African honeybees can provide insight into
the microevolutionary processes involved
in population differentiation, both in terms
of stochastic processes such as drift and
migration, but especially in terms of
morphological, behavioural and physiological
adaptations to different local conditions.
The African bees are smaller than the
European subspecies, and form a more
homogeneous cluster in multivariate space
according to PCA [
20
]. Recently, Hepburn
and Radloff [
12
] discussed the
morphological variation in a different context, by
analysing in detail patterns of spatial
variation and admixture among spatially
contiguous populations on a regional basis. In
this paper, the main objective is to expand
this (...truncated)