Genetics and bee conservation: telling the full story of a species’ decline

This post belongs to a series written by students in the Conservation Biology course BSC4052 at the University of South Florida. This course provides an overview of major themes in conservation practice and related applied problems in biology, including: population ecology in the context of conservation, patterns of diversity, valuing diversity, threats to diversity, management actions and strategies for preserving diversity.

Author: Arturo Santos is an undergraduate at the University of South Florida majoring in Environmental Biology. He is interested in insect ecology, biodiversity, and biology and enjoys identifying and documenting insects on sites such as BugGuide and iNaturalist.

We’ve all probably watched bees engage in pollination as they move from flower to flower collecting pollen.

This process is essential to the reproduction of many plants, including crops. When most people think of pollinators, they think of the honey bee (Apis mellifera). However, more than 20,000 species of bees have been described—all of which are pollinators! In fact, honey bees are actually native to southeast Asia and have spread across the globe due to human activities, potentially competing with other bees. Despite the honey bee’s ubiquity and popularity, native bees are important pollinators because ecological adaptations that differ from those of honey bees. For example, the tongues of many native bees such as bumble bees can reach the nectar of longer flowers for pollination better than the honey bee.

Among native bees, bumblebees are some of the most easily recognized. However, despite the importance of bumblebees in pollinating several crops, bumblebees are declining throughout the world. This is due to a combination of factors from habitat destruction to the introduction of non-native pathogens by introduced bees. As a result, many bumblebee species have even been declared extinct in recent decades. This is expected to worsen with the onset of rapid climate change, which can also change the geographic range of species. Bumblebee declines have clearly been recorded in Europe and North America, but evidence is lacking for South America. In a new 2018 study, Françoso and colleagues provide insight into the projected change in geographic range due to climate change in two bumblebee species from Brazil: Bombus morio and Bombus pauloensis.

What’s in a species and why does it matter?

In 1758, famous scientist Carl Linnaeus developed the Linnaean classification system that describes relationships between animals using bins like kingdom, phylum, class, order, family, genera, and species. In reality, characterizing organisms is often not as discrete. Sometimes, a species may include two groups of individuals that differ in geographic and climatic preferences. In these cases, the species is best further divided into more specific groups, such as phylogeographic lineages. In the field of phylogeography, historical, genetic, and geographic data are used to determine how two populations of a species came to occupy their unique geographic distribution. A phylogeographic lineage is thus a population of a species that is somewhat geographically isolated from another (Arbogast, 2001). In 2016, Françoso and colleagues found Bombus morio to lack a separation into phylogeographic lineages but found three for Bombus pauloensis. Species are often considered as a single unit if their geographic ranges expand, but the truth may be that only some phylogeographic lineages are expanding while others are declining (D’Amen et al, 2013). The authors speculated that the differing geographic and climatic preferences of the three phylogeographic lineages in Bombus pauloensis may affect how they will each fare in climate change despite all being members of the same species.

Some lineages are more susceptible than others

To determine the fate of each lineage, the authors used data collected on the geographic distribution of those lineages and information about climate change (Françoso et al., 2016). Françoso and colleagues (2018) then analyzed this 2016 data to project geographic range expansion or decline for each lineage using computer models. The researchers found that both species are projected to experience a contraction in range as suitability of their habitats decline. By 2070, the ranges of both B. morio and B. pauloensis were expected to decline by 45% and 49%, respectively, assuming that the climate change predictions hold up. For the phylogeographic lineages of B. pauloensis, the researchers hypothesized that the lineages closer to the periphery of their species’ range will be projected to suffer a greater decline because they occupy the edge of their species’ range and will most likely be the first to perish if habitat quality worsens. Their hypothesis was confirmed by their data. The lineage of B. pauloensis closer to the center of the species’ range was projected to have its range decline by 37%. A more northern, peripheral lineage was projected to decline by 71% and a southern lineage by 60%. Clearly, the lineage of B. pauloensis closer to the center of the geographic distribution appeared to be shielded from decline relative to the other lineages, supporting the claim that two different phylogeographic lineages can respond differently to climate change.

The Course of Action

How does this information help conservation for these bumblebees? The authors propose establishment of a refuge east of São Paulo and Rio de Janeiro in Brazil. The refuge has already been proposed by other studies to conserve other organisms, many of which are exclusively found in this area. The researchers suggest that protecting this refuge will not only preserve the pattern of biodiversity but also the wider ecological circumstances that support it. Nevertheless, these findings add important perspectives to conservation issues that scientists should consider in the future.

Feature image: Bumblebees are important pollinators of natural flora and managed crops. Unfortunately, many bumblebee species are currently in decline with some having even gone extinct in recent decades. Source: Wikimedia Commons

References

Arbogast, B. S. 2001. Phylogeography: the history and formation of species. American Zoologist, 41(1): 134-135. https://doi.org/10.1093/icb/41.1.134

D’Amen M, Zimmermann NE, Pearman PB. 2013. Conservation of phylogeographic lineages under climate change. Global Ecol. Biogeogr., 22: 93-104. https://doi.org/10.1111/j.1466-8238.2012.00774.x

Françoso E, Zuntini AR, Carnaval AC, Arias MC. 2016. Comparative phyleogeography in the Atlantic forest and Brazilian savannas: Pleistocene fluctuations and dispersal shape the spatial patterns in two bumblebees. BMC Evolutionary Biology 6: 267. https://doi.org/10.1186/s12862-016-0803-0

Françoso E, Zuntini AR, Arias MC. 2018. Combining phylogeography and future climate change for conservation of Bombus morio and B. pauloensis (Hymenoptera: Apidae). Journal of Insect Conservation: 1-11. https://doi.org/10.1007/s10841-018-0114-4