Modeling of population dynamics of aphids and parasitoids under the influence of the landscape and the symbiont Hamiltonella defensa.

• Grant number: 23/07437-7
• Support Opportunities: Scholarships in Brazil - Scientific Initiation
• Start date: August 01, 2023
• End date: March 31, 2024
• Field of knowledge: Biological Sciences - Ecology - Theoretical Ecology
• Principal Investigator: Carolina Reigada Montoya
• Grantee: Renan Moreira Leite
• Host Institution: Centro de Ciências Biológicas e da Saúde (CCBS). Universidade Federal de São Carlos (UFSCAR). São Carlos , SP, Brazil

Abstract

Aphids have several symbionts, both facultative and obligate, which can promote several beneficial functions. An example of a facultative symbiont frequently present in populations of different species of aphids is the bacterium Hamiltonella defensa, which protects its hosts from parasitoid attacks, increasing the survival of aphids against attacks at the cost, on the other hand, of reducing their longevity and fecundity. The presence of symbionts in aphid populations is variable and depends on several factors, including the presence of natural enemies and the host population's propagation chances. Thus, the advantage of harboring symbionts is related to the cost/benefit ratio provided. For example, in the presence of parasitoids, harboring H. defensa provides protection and increases the fitness of aphids, however, in the absence of these natural enemies, due to the energy loss, the presence of symbionts is no longer advantageous to individuals. The presence of symbionts also depends on the rates of vertical transmission, which is predominant and concerns the transmission of microbiota from parent to offspring, and horizontal transmission, in which microorganisms propagate throughout an entire population. The presence of symbionts can also interfere with aphid interactions with the community to which they belong. For example, the richness and abundance of plant species that compose the landscape directly affect the abundance of aphid species, indirectly affecting the abundance of parasitoids associated with them, increasing the rate of parasitism and resulting in the population reduction of aphids. These "bottom-up" and "up-down" effects are responsible for maintaining the balance of these populations, which regulate themselves through this negative feedback mechanism. Symbionts can change through demographic changes the effects of this feedback, acting as a source of differentiation and population adaptation. Considering the effects of the landscape (richness/abundance of host plants for aphids) and the presence of natural enemies on the variation and maintenance of the symbiont population in aphid populations, the aim of this study is to evaluate, through mathematical modeling, the consequences of aphid-parasitoid-symbiont interactions in landscapes with different degrees of heterogeneity.