Discussion
Impacts of commercially produced B. terrestris are more complex
in the Mediterranean region where B. t. dalmatinus is native
subspecies and large numbers of commercial colonies have been used
continuously for 25 years. In this study we divided the sampled
populations into three groups; 1) greenhouse (commercial) populations 2)
nearby greenhouses and 3) far from the greenhouses populations. We
examined the genetic structure of different commercial stocks and native
populations and assessed the degree of genetic introgression into native
populations using twenty microsatellite markers and two mitochondrial
genes. Our results demonstrate that the values ofFST between populations were not significant, and
the maximum FST value was only 0.045 (Table 3).
Therefore, commercial and native populations were not differentiable
based on twenty microsatellite markers. Similarly, structure analyses
supported this pattern. According to the best K value
(K =4), the populations are separated into four distinct clusters.
However, there are transitions between these four main clusters and it
has been determined that populations could not been clearly separated
from each other. Neighbor-Joining (NJ) trees inferred from the mtDNACOI (A) and cyt b (B) gene regions could also distinguish
groups clearly (Fig. 3). A possible reason for the observed low genetic
differentiation between commercial and wild bumblebee populations is
that although the origins of the commercial colonies were not well
known, commercial and native B. terrestris populations probably
derived from a common ancestor. A second explanation is that possible
selection process in commercial breeding strains may have not
significant impacts on the genetic differentiation between the two types
of populations. Similarly, a few previous studies of B.
terrestris showed that the mainland European B. terrestrispopulations had a relatively homogenous genetic structure but had clear
differences for some island subspecies (Estoup, Solignac, Cornuet,
Goudet, & Scholl, 1996; Lecocq et al., 2013; Widmer, Schmid‐Hempel,
Estoup, & Scholls, 1998). But a recent study on B. terrestrisshowed that Irish B. terrestris populations were highly
differentiated from British and continental B. terrestrispopulations, the latter two showing higher levels of admixture (Moreira,
Horgan, Murray, & Kakouli-Duarte, 2015). In addition, Cejas, Ornosa,
Munoz, & De la Rua (2018) recently found an effective marker
(16S ) to differentiate B. t. terrestris and B. t.
lusitanicus populations (endemic in Iberian Peninsula).
Native B. t. dalmatinus populations show considerable differences
in the life cycle patterns depending on environmental conditions. Along
the some coastal area of the Mediterranean region, native B. t.
dalmatinus populations are active from November until July. New queens
enter summer aestivation and remain dormant during the dry season until
the rainy period starts (September-November) (Gurel, Gosterit, & Eren,
2008). Therefore, life-cycle patterns of aestivated native B. t.dalmatinus populations are synchronized with the greenhouses
tomatoes production period (September-July) in coastal Mediterranean
region where the commercial colonies have been widely used. However,
aestivated native B. t. dalmatinus populations have become
extinct or rare in Mediterranean coastal areas because of both
introgressions of commercial stocks and habitat destruction, and heavy
urbanization. Some authors have also implied that commercialization
processes are capable of changing some colony traits of native B.
terrestris colonies (Gosterit & Baskar, 2016; Ings, Ward, & Chittka,
2006). The genetic introgression could lead to the loss of specific
traits and local adaptations (Evans, 2017). In this study, within the
group of the more distant populations FS is the only aestivated
population, located more than 30 km away from greenhouses areas and
occurs in the one of the best-preserved ancient cities in the
Mediterranean region. In our study, although the values ofFST between populations were not significant,
according to PCA results, FS population separated from other
populations. Therefore, we suggest that FS population should be
initially conserved to avoid extinction.
In the mitochondrial analysis, two haplotypes (haplotype A; 28.8 %
samples and haplotype B; 71.2 % samples) were found for the COIgene. While haplotype A was common in commercial populations, haplotype
B was common in both nearby greenhouses populations and far from the
greenhouses populations. In our study, six haplotypes (H1-H6) were found
for the cyt b gene. Considering haplotypes and their frequencies,
we found that the most abundant haplotype was H4, which was detected in
43 individuals (% 63.2). While haplotypes 4 and 5 are known to belong
to the B. t. dalmatinus, haplotypes 1, 2, 3 and 6 are known to
belong to both B. t. dalmatinus and B. t. terrestris.These haplotypes were found in the commercial populations and nearby
greenhouses populations. The detection of haplotypes 1, 2, 3 and 6 in
the commercial populations and nearby greenhouses populations
potentially suggests that commercial producers in Turkey either have
also been producing and selling non -native B. t. terrestris in
Mediterranean region where B. t. dalmatinus is native subspecies
or mixing B. t. terrestris and B. t. dalmatinus in order
to set up breeding stocks. We don’t know whether B. t. terrestrishas become established in the Mediterranean region where it is not
native. Some environmental factors can prevent its establishment in this
region. There is some evidence to support this. Lecocq, Rasmont, Harpke
& Schweiger (2016) considered that B. t. terrestris would be
able to survive as active colonies in south of South America, New
Zealand, southeast Australia, and Tasmania based on 19 bioclimatic
variables and implied that Mediterranean region is not climatically
suitable area for B. t. terrestris. On the other hand,because of high demand from consumers for a year-round supply of
greenhouse production, highland (at different altitudes and climatic
conditions) greenhouse tomato production in Turkey has been increasing
in recent years. Therefore, commercial B. terrestris colonies are
used for pollination all year round. We suppose that B. t.
terrestris is able to establish in the wild particularly adjacent to
the highland greenhouse areas and spread.
It will be useful for future ecological studies to determine locally
geographic areas where the establishment success of commercial queens in
greenhouses could be higher. In addition, because of morphological
similarities and difficulties, new techniques and molecular markers to
separate commercial strains, subspecies, and ecotypes and to determine
the introgressions are needed. As mentioned in previous studies (Evans,
2017; Goka, 2010; Ings, Ward, & Chittka, 2006; Koide, Yamada, Yabe, &
Yamashita, 2008), some special precautions; such as using of mesh to
cover glasshouse vents, using of queen excluders to keep gynes in the
nest and disposing of old nests to restrict the escape of males and
gynes must be taken to prevent both novel subspecies or commercial
stocks introductions and the spread of pathogens and pests. Despite some
restrictions, regulation of the movement of B. terrestrissubspecies is problematic and ineffective. We still have little
information on the origin of commercial stocks. To reduce the risk of
non native subspecies and genetically different populations and the risk
of spreading pathogens and parasites, effective control methods would
seem to be necessary even without the establishment. Furthermore, there
is an urgent need to develop conservation strategies for native bumble
bee populations.