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Can unexpected changes happen in the process of plant domestication?

This fascinating investigation takes us on a journey through the evolutionary history of the squash plants to understand how domestication has modified the characteristics of these plants and their relationships with their pollinators.

Today, to feed ourselves, we just need to go to the nearest supermarket and select the fruits and vegetables of our choice. But have you ever imagined how hard the food search was for our ancestors? Well, this process, which for us is practically unconscious, was costly for a long time for them, who not only needed to actively hunt and search for plants but also identify what was actually edible. 

To make the process easier people began to select the most interesting plants and grow them for our consumption, giving rise to agriculture. Later, they began to select characteristics of interest for plant species, such as fruit flavour, size, and nutritional components, a process known as domestication. This process has been with modern humans for a long time and has been very important in increasing and improving food production. However, changing some traits in a plant could also unexpected consequences for other traits. Human selection may result in indirect changes to factors such as flower-size, which can alter pollinator choices during resource collection. Could these changes lead to significant shifts in plant-pollinator interactions, leading to ecosystem changes? 

This question intrigued a group of researchers that investigated whether there are differences in floral morphological traits, the quantity and quality of rewards (nectar and pollen), and the visit rates and behaviour of pollinators associated with domesticated and wild squash plants (genus Cucurbita) in the tropical forests of Mexico – the centre of origin of this group. The study, recently published in the American Journal of Botany, takes us on a journey through the evolutionary history of this group of plants to learn how humans modified the characteristics of these plants and their relationships with other organisms.

Squash is widely known and consumed in different regions and cultures around the world. Readers who enjoy cooking will know that we can use a large part of this plant for consumption, including seeds, fruit, and flowers that yield delicious recipes. Something less known, is that this plant is also appreciated by bees from the genus Eucera which developed, approximately 10 million years, a highly specialised relationship with the wild lineages of the squash plant. These bees synchronise their phenology and foraging with the flowering period and anthesis time of the squash flowers. This occurs through evolutionary adaptations that may include responses to visual, olfactory stimuli and variations in environmental temperature. The relationship is so close that it’s the foundation of the next generation of bees. An unbelievable association, isn’t it? Besides, these bees assure the reproductive success of the Cucurbita, being considered efficient pollinators of this plant, meaning that everyone wins in this relationship!

A bee covered in pollen enters a squash flower.
Eucera (Peponapis) sp. into squash flower. Photo by Leopoldo Vazquez. Photo reproduced by kind permission.

However, 10,000 years ago, something happened that altered this specialized interaction between Cucurbita and their pollinators: the first artificial selections that resulted in the squash species’ domestication. This process led to some desired changes, such as an increase in the size of fruits and seeds concerned. Nonetheless, over the years, could this selective process also indirectly change the floral traits and the propriety of the resources collected by bees in cultivated squash plants? Furthermore, could these differences between cultivated and wild plants influence the interactions of these plants with their pollinators?

The answer to these questions seems clear: yes, they could! The authors provided evidence for this by showing that the two cultivated varieties of Cucurbita share more floral morphological traits with each other than with the wild species, suggesting the differentiation of these characteristics throughout the process of domestication. In addition, the domestication of this plant resulted in larger flowers, higher amount and protein content of the pollen, and increased nectar accumulation over time compared to the wild Cucurbita plants. All these characteristics are commonly associated with a greater attraction of pollinators and, despite having similar communities of floral visitors, the cultivated plants were indeed more attractive to bees, including specialists of the genus Eucera. Therefore, it’s important to think about the conservation of wild Cucurbita plants and their specialized association with Eucera bees. For this, it is essential to maintain the ancestral populations of this plant in their centre of origin, preserving their interactions with these pollinators.

A scramble of lines between pollinators and plants. However some lines like the lines between Peponapis bees and plants are notably thicker.
Interaction network between wild (CAS) and cultivated (CAA and CM) plants of Cucurbita species and their pollinators. It is possible to observe a greater intensity (line width) of interaction and links of the specialist bees Eucera (Peponapis) sp. with cultivated plants. Figure from Glasser et al. (2023)

This study provides a fascinating example of how domestication, besides selecting characteristics of interest, can also result in unexpected shifts in floral traits. These changes may give place to more attractive flowers that are visited more frequently by a greater number of pollinators, which in turn increases the reproductive success of cultivated plants. Altogether, these results illustrate that we are constantly changing ecosystems and processes based on our decisions, even when unintentional.

Glasser, S. K., Santiago‐Hernández, M. H. D., Delgado‐Carrillo, O., Espino, L. A. V., Pérez, A. C., González‐Rodríguez, A., Lira-Saade, R & Quesada, M. (2023). “Influence of plant domestication on plant‐pollinator interactions: floral attributes and floral visitor communities in wild and cultivated squash plants”. American Journal of Botany. 110(5): e16170. Available at: https://doi.org/10.1002/ajb2.16170

Ingrid N Gomes

A young lady smiling by the waterfront.

Ingrid (she/her) is a Brazilian Ph.D. Student at the Program of Ecology, Conservation and Wildlife Management at Universidade Federal de Minas Gerais (Brazil). She’s interested in studies related to Pollination Biology with a focus on interactions between bees and plants, Urban Ecology, Conservation, and Science Communication.

Traducción al español por Carlos A. Ordóñez-Parra.
Traduction française par Ingrid. N. Gomes.
Tradução ao português de Ingrid. N. Gomes.

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