A field note on Monarch butterflies

Monarch butterfly on Baccharis solicifolia

By Carlos Alvarez-Pereyra, biologist. 

Last August, me and a colleague were sampling plants in one of Saltillo’s arroyo named “El Cuatro” back in northern Mexico..

Among several flowering plants in and out the bed of this arroyo we noticed that flowering Baccharis was visited by harvesting honey bees (Apis mellifera) and feeding Monarch butterflies (Danaus plexippus) at midday.

The presence of at least one migrating Monarch in this time of the year is quite rare because migration normally starts late October – early November in this latitude. Residents honey bees harvest all year long on all kind of flowers.

Honeybees on Baccharis

Baccharis salicifolia is a blooming shrub native to the desert southwest of the United States and northern Mexico, as well as parts of South America. This is a large bush with sticky foliage which bears plentiful small, fuzzy, pink or red-tinged white flowers which are highly attractive to butterflies.

I thought it could be helpful to some colleague working with these species somewhere in the world.

Pollination facilitation and temporal changes of plant-floral visitor network in a serpentine shrubwood of Cuba

Shrubwood Lomas de Galindo

By Alameda et al.

Pollination is an essential ecological interaction for the life cycle of plants and the nutrition of pollinating animals. Most animal species that pollinate flowers are insects, especially butterflies, moths, bees, and flies. These interactions change during the day and night, between seasons, and vary across different ecosystem types. In the stressful ecosystems for plants, scientists consider the fundamental interactions to be facilitative rather than competitive.

In this study, we analyzed whether this theory held in a semi-desert ecosystem in Cuba, the largest island in the Caribbean. We also described how interactions between pollinators and plants varied throughout the year, month by month. In Cuba, there are only two seasons: the rainy season and the dry season. We describe diurnal interactions, not nocturnal ones.

We found that the dynamics of pollination interactions were highly variable throughout the year. The composition and structure of the pollination interaction network changed each month. We found that some plants function as the core of interactions and are essential for maintaining the pollination service. For example, Agave offoyana is a core species in the dry season. Furthermore, the bees Apis mellifera and Melipona beecheii were the core pollinators in the interactions.

The plants that cluster most of the interactions do not do so at the same time of year, but rather alternate between them. This is evidence of a facilitating mechanism in this type of semi-desert ecosystem where water availability is limited. Our results identified key plant and pollinator species that must be conserved to maintain the pollination service in this ecosystem.

Read the scientific article in JPE 

Spanish version

La polinización es una interacción ecológica esencial para el ciclo de vida de las plantas y la alimentación de los animales polinizadores. La mayoría de las especies animales que polinizan las flores son insectos, especialmente mariposas, polillas, abejas y moscas. Estas interacciones cambian durante el día y la noche, entre las estaciones y varían en los diferentes tipos de ecosistemas. En los ecosistemas más estresantes para las plantas, los científicos consideran que las interacciones fundamentales son de facilitación, no de competencia.

En este estudio analizamos si esa teoría era cierta en un ecosistema semidesértico de Cuba, la mayor isla del Caribe. Además, describimos cómo las interacciones entre polinizadores y plantas variaban entre meses durante todo un año. En Cuba existen solamente dos estaciones, la estación lluviosa y la estación seca. Describimos las interacciones diurnas, no las nocturnas.

Encontramos que durante el año la dinámica de las interacciones de polinización eran muy variables. Cada mes cambiaba la composición y la estrucutura de la red de interacciones de polinización. Encontramos que algunas plantas funcionan como núcleo de las interacciones y son esenciales para mantener el servicio de polinización. Por ejemplo, Agave offoyana es una especie núcleo en la estación seca. Además, las abejas Apis mellifera y Melipona beecheii fueron los polinizadores núcleo en las interacciones.

Las plantas que agrupan la mayoría de las interacciones no lo hacen en el mismo momento del año, sino que se relevan temporalmente. Esto es una evidencia de un mecanismo de facilitación en este tipo de ecosistema semidesértico donde hay poca disponibilidad de agua. Nuestros resultados detectaron a las especies de plantas y polinizadores claves que deben ser conservados para mantener el servicio de polinización en este ecosistema.

The fate of pollen in two morphologically contrasting buzz-pollinated Solanum flowers

Pathways depicting the fates of pollen in a bee pollinated species such as the ones studied here. The diagram shows pollen contained inside the anthers (yellow); pollen removed that can be potentially transferred to conspecific stigmas (blue); pollen lost from the fertilization process, including dislodged pollen that falls to the ground and pollen stored by the bee (e.g., in corbiculae) and thus unable to contribute to fertilization (red); and pollen deposited on stigmas (green). Created with BioRender.com.

 

by Vasquez-Castro et al.

The fate of pollen describes what happens to pollen once it is removed from a flower. Studying it is crucial to understand how much pollen is lost during pollination and how efficiently it reaches other flowers. Another key aspect of pollination is how many pollen grains from one donor flower reach the stigmas of a sequence of other flowers. This helps us understand how far pollen grains can travel, and ultimately, how plants mate.

We studied both aspects of pollination under laboratory conditions with bumblebees visiting two species of flowers with contrasting morphology: Solanum rostratum and S. dulcamara. Both species are buzz-pollinated, meaning they require bee vibrations to release pollen, and they do not provide nectar to pollinators.

We found that both species had very low pollen transfer efficiency (~1 %), as is typical for most plants. Many pollen grains were deposited on the first flower visited, with fewer and fewer reaching subsequent flowers. This means that pollen is used up quickly, limiting how far it can travel between flowers. We also found that our two species showed very different pollen fates, likely explained by their contrasting floral characteristics. This highlights that future studies should investigate how flower morphology impacts pollen fates.

Read the scientific article in JPE