César Ramiro Martínez-González & José de Jesús Morales-Sandoval
The genus Opuntia belongs to the Cactaceae that is characterized by having flattened stems known as cladodes, each one being similar in shape to a tennis racket. Plants of this genus are commonly known as nopales (in Spanish) or prickly pear (in English), which are used for human consumption as well as their fruits, which can be sweet (tunas) or acid (xoconostles). Similarly they are widely used as livestock feed, various industrial applications (adhesives, resin and waterproofing) and medically as precursors of some drugs. Prickly pears like all cacti are distributed naturally throughout the American continent and naturalized in many countries of the world. It is thought that prickly pears have their centre of origin and diversification in Mexico, where there is no consensus on how many species there are, since this depends on the specialized literature that is consulted.
Using a grant funded by the British Cactus and Succulent Society, Opuntia lasiacantha (Figure 1) and Opuntia rzedowskii (Figure 2) were studied, two species that are different, but for a long time some authors believed that they were the same species. We write “they believe” because detailed work had never been done on the two species to determine whether they were the same or two different species.
We analyzed morphological characters such as cladode size, spines, flower colour and fruit size, as well as their DNA to examine their relationship. The results obtained confirmed that they are two different prickly pear-producing species (Figures 1B–C and 2B–C). This research will be published in greater detail in the scientific journal Bradleya.
We thank all the members of the society since through the British Cactus and Succulent Society we received the finances to be able to carry out the fieldwork, characterize the entire life cycle of the two species (habit, mature cladode, juvenile cladode, flower and fruit) and obtained their genetic material. In order to be able to conserve these species it was first necessary to obtain the knowledge about which species exist.
We invite all readers interested in the subject to learn a little more about this fascinating and difficult plant group. For this we recommend the following publications, where you will find detailed information about the characteristics, habits, classification, distribution and uses of these prickly pears:
- Barbera, G., Inglese, P. & Pimienta Barrios, E., (eds.) (1995). Agro-ecology, cultivation and uses of cactus pear. FAO Plant Production and Protection Paper No. 132. FAO, Rome.
- Bravo Hollis, H. (1978) Las cactáceas de México. Vol. 1. National Autonomous University of Mexico, Mexico City.
- Bravo Hollis, H. & Scheinvar, L. (1995). El interesante mundo de las cactáceas. National Council of Science and Technology, Mexico.
- Hunt, D. (ed.) (2014). Further Studies in Opuntioideae (Cactaceae). Succulent Plant Research. Vol. 8.
- Inglese, P., Saenz, C., Mondragon, C., Nefzaoui, A. & Louhaichi, M. (eds.) (2017). Crop ecology, cultivation and uses of cactus pear. ICARCA-FAO, Rome, Italy.
- Majure, L., Puente, R., Griffith, M.P., Judd, W.S., Soltis, P.S. & Soltis, D.E. (2012). Phylogeny of Opuntia s.s. (Cactaceae): clade delineation, geographic origins, and reticulate evolution. American Journal of Botany 99(5):847-864.
Pollination biology of Stenocereus queretaroensis and the importance of bat pollination services
Connie Tremlett, University of Southampton, UK
Techaluta de Montenegro is a small town nestled in an incredible landscape in Jalisco, Mexico, framed on one side by forest-clad mountains and on the other by a seasonal lagoon which generates impressive dust-bathed red sunsets during the dry season. Columnar cacti play a keystone role throughout this landscape, providing food and structural resources to animals such as bats, birds and rodents. One such is a species of arborescent columnar cactus endemic to this region of central western Mexico, Stenocereus queretaroensis, which has been hugely important for the subsistence of local people for centuries, and is now cultivated commercially for its fruit (the pitaya), providing one of the main income streams for the town.
With the help of a research grant from the BCSS, I visited the town to find out more about the pollination biology of this cactus to help inform local management. In 2016 we set up exclusion experiments on cacti in pitaya plantations and on ranches, by placing bags of different mesh sizes over flowers during the day and/or night to expose the flowers to certain pollinators only. So, for example, the bags could prevent birds and insects from accessing flowers during the day, but allow bats to reach them at night – or vice versa. We monitored the flowers to record whether they successfully developed into fruits, and collected the fruits to weigh them and count the number of seeds they contained.
Though many people think of bees and other insects when picturing pollinators, bats are important pollinators in tropical regions, and many species of columnar cacti in Mexico have a close relationship with nectar-feeding bats. In our study, we found that pollination by bats not only increased fruit yield for pitaya farmers, but also increased the size of fruits (thereby increasing the value of fruits as bigger fruits are sold at higher prices) and seed set. The principal pollinator is Leptonycteris yerbabuenae, the lesser long-nosed bat, a migratory species which travels along ‘nectar corridors’ between Mexico and the USA, pollinating many species of cacti and agaves en route.
This has important implications in a region where bats are commonly persecuted, due in part to the mistaken belief that all bats are ‘vampiros’, vampire bats, which can transmit rabies to cattle. Our research has shown local farmers and landowners that in order to maintain both fruit production on farms, and wild populations of Stenocereus queretaroensis (whose population in the area is already suffering the negative impacts of agricultural activities), then bat populations must be conserved, and the use of pesticides – which are toxic to bats – avoided.
You can read more about this research in our open access paper published in the Journal of Applied Ecology, “Pollination by bats enhances both quality and yield of a major cash crop in Mexico” found at https://doi.org/10.1111/1365-2664.13545.
Our grant from the BCSS also helped my research team (a collaboration between the University of Southampton, UK, and CIIDIR Durango, Instituto Politécnico Nacional, Mexico) carry out research to explore how the economic benefits of bat pollination to pitaya production are distributed between different social groups; and also to investigate which other species of cactus are pollinated by nectar-feeding bats and the implications for pollination networks. Stay tuned for the results!