Ceratina calcarata on a stem
Newswise — TORONTO, May 15, 2023 – Researchers at York University have discovered that wild bees living in cities like Toronto face more challenges and problems from their environment than bees in rural or suburban areas. These challenges include things like diseases and pests.
The researchers also found that wild bees living in highly urbanized areas and areas with fewer natural habitats experienced changes in their microbial communities. These changes make it harder for the bees to find food, suitable places to build nests, and potential mates.
As cities continue to grow and landscapes change, these environmental challenges for wild bees are expected to become even more severe. This poses a significant threat to the natural ecosystems of bees and their biodiversity. By 2050, it is projected that about two-thirds of the world's population will be living in cities, further exacerbating these challenges.
According to Sandra Rehan, an associate professor at York University's Faculty of Science and the corresponding author of the study, having fragmented habitats in densely urban areas has negative consequences. It not only reduces genetic diversity due to increased inbreeding but also leads to a higher diversity of pathogens. This means that bees living in cities are more vulnerable to various diseases and infections caused by these pathogens.
The researchers conducted a study on a species of wild bees called common carpenter bees (scientifically known as Ceratina calcarata). They examined the genetic information of 180 individual bees using a method called whole genome sequencing. The study focused on understanding the population genetics, as well as the metagenome (genetic material of the microorganisms) and microbiome (microbial communities) of these bees. The researchers also investigated how environmental stressors affect the bees in different locations within the Greater Toronto Area. It's important to note that these bees are native wild bees and not managed or non-native bees like honeybees.
They also found significant environmental variation in bee microbiomes and nutritional resources even in the absence of genetic differentiation.
Katherine D. Chau, the lead author of the study and a PhD student at York University, highlights that infections caused by parasites and pathogens play a significant role in the decline of bee populations worldwide. Urbanization, habitat loss, and habitat degradation further worsen this issue. However, Chau suggests that cities have the potential to take actions to assist wild bees.
“We found the best way to connect bee habitats and create conditions for more genetic diversity is through green spaces, shrubs and scrub. Conservation efforts focussed on retaining and creating these habitat connectors could go a long way toward helping wild bee health.”
It's important to recognize that while bees are well-known pollinators, cities can have an impact on all insect pollinators. These insects play a crucial role in pollinating over 87 percent of flowering plants and 75 percent of global food crops. Unlike rural areas, cities experience what is known as the urban heat island effect, where temperatures within the city are higher than in the surrounding areas. This effect can affect the timing of flowering and the length of the growing season. As a result, there is a risk that flowers may bloom either before or after bees are active and searching for food. This mismatch in timing can have implications for the pollination process.
The higher number of pathogen and parasite infections in urban areas can also be attributed to disease spill over. Because the bees are concentrated in certain areas, infected bees are more likely to contaminate the flowers they visit, which then spreads the infection to the next bee that visits that flower, even across bee species, say the researchers.
According to Sandra Rehan, the study conducted by the researchers is the first known investigation that combines whole genome sequencing, population genomics, and metagenomics of a wild, solitary bee in an urban environment. The study aims to understand the intricate relationship between bees, metagenomic interactions (interactions with microorganisms), and densely populated urban landscapes. This approach not only helps in evaluating the overall well-being of wild bees in urban areas but also has the potential to be applied to various wildlife and landscapes, providing valuable insights into their health and ecological dynamics.
Now that several known bee and plant pathogens have been identified in dense urban areas, the researchers say it paves the way for early detection and monitoring of threats to wildlife in cities.
“Future studies should explore the link between reduced genetic diversity and the fitness of wild bees in cities,” says Chau.
The paper, Integrative population genetics and metagenomics reveals urbanization increases pathogen loads and decreases connectivity in a wild bee, was published in the journal Global Change Biology.
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