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Pattern of species richness in the New World Triatominae

Of the five tribes within the Triatominae subfamily, Triatomini and Rhodniini include 88% of the recognized 150 species. Within the two most numerous tribes, the genera Rhodnius, Panstrongylus, and Triatoma constitute 86.5% of the species found in the Americas. Controversies about the evolution of the Triatominae still exist, although there is ample evidence supporting its polyphyletic constitution. The Rhodnius species are generally associated with palm tree species found in the geographic range from southern Amazonia to Central America. The majority of the 13 Panstrongylus species are exclusively sylvatic with a wide variety of habitats and wild animals. Triatoma is the most numerous genus, including 80+ species distributed as far as the extreme northern and southern latitudes. Recent evidence suggests that Triatoma species of Central and North America constitute a group that evolved independently from the Triatoma species of South America.12

A study considering 118 Triatominae species of the New World showed that groups analyzed at the continental scale had patterns of species richness that showed a significant linear latitudinal gradient with low values at the extreme latitudes and highest values near the equator (precisely on the 5-10° southern latitudinal band). The study also showed that species richness is significantly associated with habitable geographic area and temperature in the Southern hemisphere; in this hemisphere, there is a significant longitudinal gradient given by the Andes range, an element that influences the increase of species richness toward the east of South America.23

We expanded the analysis of the data used by Rodriguero and Gorla23 and used a similar methodology to analyze the latitudinal range for the species (difference between maximum and minimum latitude of the species geographic distribution). The results showed a significant linear increase of the latitudinal range of the species from the equator (i.e., narrower near the equator, wider toward higher latitudes), as predicted by the Rapoport’s rule (Fig. 9.1). When considering the species richness across the latitudinal regions of the most numerous Triatominae genus, it is clear that individual genera do not follow the same pattern shown by the complete set of Triatominae species. For instance, Triatoma shows a bimodal pattern of species richness with low frequency at low latitudes and modal maxima at around 23° north or south. Rhodnius shows an unimodal species richness distribution but strongly skewed with modal number of species located on the Northern Hemisphere at low latitudes and a few species on the Southern Hemisphere, some of them reaching the 30° southern latitude. Panstrongylus also shows a unimodal species richness distribution with the majority of species located on the Southern Hemisphere (Fig. 9.2).

Relationship between the average latitudinal range and the midpoint of the latitudinal range for Triatominae species in the Americas

Figure 9.1 Relationship between the average latitudinal range and the midpoint of the latitudinal range for Triatominae species in the Americas. Vertical and horizontal lines over the points indicate standard errors.

Species richness of Triatominae per 10° latitudinal band

Figure 9.2 Species richness of Triatominae per 10° latitudinal band. (A) Triatoma species; (B) Rhodnius species and Psammolestes species; (C) Panstrongylus species; (D) Old World Triatominae; (E) Dipetalogaster, Eratyrus, Hermanlentia, Alberproseniini, Bolboderini, and Cavernicolini. Negative latitudinal bands are in the Southern Hemisphere.

In a more recent analysis, the geographical ranges and richness patterns of Triatominae richness in Latin America was analyzed,24 using spatial eigenvector mapping, multiple regressions, and generalized linear models. They found that richness and species ranges show high correlation and identified an important role for temperature and temperature seasonality in explaining richness and distributions.

 
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