The more you have, the more you get. It is a principle, even written in the Bible (Parable of the Talents; Matthew 25:14). In ecology, this principle can be translated in different ways, one of which was the focus of our study. We were interested in testing whether species which have wider niches also had wider geographic ranges. This is known as the range size-niche breadth hypothesis, for which there has been mixed support in empirical studies [1,2].
Our study organisms were nothing less than the ominous Triatominae, also known as the assassin bugs, vampire bugs, or kissing bugs. Many of the species within this group are vectors of Chagas disease which is a major public health concern in the Americas. It has even been hypothesised that Charles Darwin contracted Chagas disease during his voyage in the Beagle through South America [3]. In fact, Chagas disease is quite alarming. The World Health Organization estimates that over 70 million people are exposed to higher risks of Chagas disease across the Americas [4]. It is not surprising that approximately 6 million people are affected by the disease. More strikingly, 9,000 newborns become infected with Chagas during gestation. Thus, the Triatominae are interesting not only from an ecological perspective, but also from a public health one.Â
Assembling the most comprehensive dataset of feeding patterns to date, we set out to test whether climate and/or diet were correlated with geographic range for 61 species of Triatominae. Our estimates of diet breadth were highly accurate too, being curated from >140 studies which used PCR and ELISA as methods of identification of hosts. One finding that struck me was the fact that some species feed on highly “unusual” (to me) hosts, such as fish and cockroaches! Our analysis covered virtually all corners of the Americas where these bugs can be found (Fig 1; adapted from Caron et al. 2024; PLoS Negl. Trop. Dis [5]).
Figure 1. Triatominae are distributed across the Americas and are vectors of Chagas disease, a major neglected tropical disease. Adapted from Caron et al (2024) PLoS Negl Trop Disease
Surprises aside, our findings were revealing. Precipitation and temperature niche breadths were positively correlated with geographic range size even after accounting for the non-independent, phylogenetic relationship between species (failing to control for this could lead to artifacts!). However, diet breadth was not correlated with geographic range size, suggesting that species that can use multiple host species do not necessarily distribute themselves more widely. These findings provide mixed support for the range size-niche breadth hypothesis: on the one hand, it is supported in climatic niches but on the other hand, there are no support when it comes to diets (Fig 2; adapted from Caron et al. 2024; PLoS Negl. Trop. Dis [5]).
Figure 2. Diet breadth is not correlated with range size (left panel) but temperature breadth (centre) and precipitation breadth (right panel) are. Dashed regression line indicates lack of statistical significance. Statistical significance measured at threshold level of p < 0.05 (solid lines). Adapted from Caron et al (2024) PLoS Negl Trop Disease
In the future, we need to know how the joint distribution of hosts and bugs shape Triatominae’s geographic range because it is possible that species that use more hosts, might use hosts that are themselves more narrowly distributed. However, at this stage, we do not have the data to test this hypothesis. While we do not have a definitive answer in favour of, or against, the range size-niche breadth hypothesis, our study open new ways of understanding the ecology of an important, yet understudied group of insects that can be vectors of a deadly disease affecting the Americas.
References cited
Brown JH. On the Relationship between Abundance and Distribution of Species. Am Nat. 1984;124(2):255–79.
Slatyer RA, Hirst M, Sexton JP. Niche breadth predicts geographical range size: a general ecological pattern. Kleijn D, editor. Ecol Lett. 2013;16(8):1104–14.
Simpson GG. Charles Darwin in search of himself. Sci Am 1958;199:117–22.
https://www.paho.org/en/topics/chagas-disease#:~:text=Chagas%20disease%20is%20a%20parasitic,considered%20a%20neglected%20tropical%20disease.
Caron FS, Rivadeneira D, Rabinovich J, Pie MR, Morimoto J (2024) Range size positively correlates with temperature and precipitation niche breadths but not with dietary niche breadth in triatomine insects, vectors of Chagas disease. PLoS Negl Trop Dis 18(8): e0012430. https://doi. org/10.1371/journal.pntd.0012430
Poster image credit and caption: Triatoma sanguissuga in Dallas, Texas. Photo credit:Â Brett Hondow