Morphology, Life Cycle, Environmental Factors and Fitness – a Machine Learning Analysis in Kissing Bugs (Hemiptera, Reduviidae, Triatominae)

Jorge E Rabinovich

doi:10.3389/fevo.2021.651683

Abstract

Populations are permanently evolving and their evolution will influence their survival and reproduction, which will then alter demographic parameters. Several phenotypic, life history and environmental variables are known to be related to fitness measures. The goal of this article was to look into the possible types of those relationships in insects of the subfamily Triatominae, vectors ofTrypanosoma cruzi, the causative agent of Chagas disease. After an exhaustive literature review of 7,207 records of publications referring exclusively to all possible features of the triatomines, using 15 keywords those records were reduced to 2,968 publications, that were analyzed individually; after deleting those publications that did not have the data in quantitative form as needed for the objective of this article, I found that 171 papers were adequate for the present analysis. From them I compiled a dataset of 11 variables and 90 cases from 36 triatomine species. Those variables included four environmental, two life cycle, and four morphological variables, and one demographic parameter: a fitness measure (the population intrinsic rate of natural increase,r0), used as dependent variable. However, the relationship betweenT. cruziand its vector host was not included in this analysis despite triatomine-T. cruziinteractions constitute an important factor in the evolution of triatomine’s life history. I resorted to the Random Forest method as a machine learning approach for the analysis of this dataset, and found that –in addition to the triatomine species themselves– only the two life cycle variables (mean development time from egg to adult, and mean fecundity, expressed as the average number of female eggs laid per female per day) were statistically significant in determining fitness (r0). The machine learning approach used in the analysis provided a similar but deeper insight into these relationships than classical regression. Except for an analysis on senescence, this is the first study in triatomines addressing these questions. These results will be useful for other theoretical optimization approaches (frequency-dependence, density-dependence, evolutionary game theory, and adaptive dynamics), thus contributing to the theoretical framework for interpreting the succession of stages in insect adaptations, a framework yet to be constructed.

Highlights

Populations of different species are permanently evolving and their evolution will influence the survival and reproduction of its members, influencing demographic parameters (Hendry, 2015)
Phenotypic selection seems to work differently between wild and captive conditions (Kingsolver et al, 2001), while a significant part of the data available relating morphology, demography, life cycle, and environmental conditions comes from laboratory-reared animals
I summarize some strongly suggestive evidence of these relationships in triatomines. The analysis of these relationships would contribute to the theoretical framework of life history evolution, and provide knowledge useful for the control of Chagas disease transmission: triatomine species have shown to be in permanent adaptation to environmental modifications, evidenced by changes in phenotype, life history, and population dynamics

Summary

Introduction

Populations of different species are permanently evolving and their evolution will influence the survival and reproduction of its members, influencing demographic parameters (Hendry, 2015). The Triatominae (Hemiptera: Reduviidae), commonly known as kissing bugs, are vectors of the parasite Trypanosoma cruzi (Chagas, 1909), the causative agent of Chagas disease This group of insects feeds primarily on vertebrate blood after evolving from predatory reduviid bugs, most likely in the New World; triatomines diversified extensively across the Americas and in parts of Asia and Oceania, being represented by over 130 species (Araujo Monteiro et al, 2018). E.g., Bello-Bedoy et al (2019), in the triatomine Dipetalogaster maximus, measured and compared among nymphal stages and adults and, between sexes phenotypic traits linked to some functions: the proboscis length and width in feeding; the head length and width in vision; the pronotum width and length in mobility, and the abdomen length in feeding capacity and fecundity These authors found sometimes a steady increase and sometimes an abrupt increase in some of those measurements, with some important effects on the functions evaluated. As in this analysis the measurements were limited to the adult stage of triatomines, we could not include the element of ontogeny

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Conclusion