The latitudinal diversity gradient (LDG), or the trend of higher species richness at lower latitudes, has been well documented in multiple groups of free-living organisms. Investigations of the LDG in parasitic organisms are comparatively scarce. Here, I investigated latitudinal patterns of parasite diversity by reviewing published studies and by conducting a novel investigation of the LDG of helminths (parasitic nematodes, trematodes and cestodes) of cricetid rodents (Rodentia: Cricetidae). Using host-parasite records from 175 parasite communities and 60 host species, I tested for the presence and direction of a latitudinal pattern of helminth richness. Additionally, I examined four abiotic factors (mean annual temperature, annual precipitation, annual temperature range and annual precipitation range) and two biotic variables (host body mass and host diet) as potential correlates of parasite richness. The analyses were performed with and without phylogenetic comparative methods, as necessary. In this system, helminths followed the traditional LDG, with increasing species richness with decreasing latitude. Nematode richness appeared to drive this pattern, as cestodes and trematodes exhibited a reverse LDG and no latitudinal pattern, respectively. Overall helminth richness and nematode richness were higher in areas with higher mean annual temperatures, annual precipitation and annual precipitation ranges and lower annual temperature ranges, characteristics that often typify lower latitudes. Cestode richness was higher in areas of lower mean annual temperatures, annual precipitation and annual precipitation ranges and higher annual temperature ranges, while trematode richness showed no relationship with climate variables when phylogenetic comparative methods were used. Host diet was significantly correlated with cestode and trematode species richness, while host body mass was significantly correlated with nematode species richness. Results of this study support a complex association between parasite richness and latitude, and indicate that researchers should carefully consider other factors when trying to understand diversity gradients in parasitic organisms.

We present an updated checklist of ectoparasite species (including mites, ticks, lice, and fleas) infesting cricetid and heteromyid rodents (Rodentia: Cricetidae and Heteromyidae) in México. For each parasite species, we include information on parasite taxonomy, host associations, collection localities, citations from the literature, and museum collections, when available. We recorded more than 172 mite, 114 flea, 22 tick, and 22 louse species from a minimum of 110 host species (82 cricetid and 28 heteromyid species) distributed across 31 states in México. This work represents the most up-to-date and comprehensive checklist of ectoparasite species parasitizing cricetid and heteromyid rodents in México.Presentamos una lista actualizada de especies de ectoparásitos (ácaros, garrapatas, piojos y pulgas) que infestan roedores cricétidos y heterómidos (Rodentia: Cricetidae y Heteromyidae) en México. Para cada especie de parásito, incluimos información sobre la taxonomía de los parásitos, asociaciones con el hospedero, localidades de colecta, citas de la literatura y colecciones de museo, cuando están disponibles. Registramos más de 172 especies de ácaros, 114 pulgas, 22 garrapatas y 22 piojos de un mínimo de 110 especies de hospederos (82 especies de cricétidos y 28 heterómidos) distribuidas en 31 estados de México. Este trabajo representa la lista más actualizada y completa de las especies de ectoparásitos que parasitan a los roedores cricétidos y heterómidos en México

Long-term data allow ecologists to assess trajectories of population abundance. Without this context, it is impossible to know whether a taxon is thriving or declining to extinction. For parasites of wildlife, there are few long-term data—a gap that creates an impediment to managing parasite biodiversity and infectious threats in a changing world. We produced a century-scale time series of metazoan parasite abundance and used it to test whether parasitism is changing in Puget Sound, United States, and, if so, why. We performed parasitological dissection of fluid-preserved specimens held in natural history collections for eight fish species collected between 1880 and 2019. We found that parasite taxa using three or more obligately required host species—a group that comprised 52% of the parasite taxa we detected—declined in abundance at a rate of 10.9% per decade, whereas no change in abundance was detected for parasites using one or two obligately required host species. We tested several potential mechanisms for the decline in 3+-host parasites and found that parasite abundance was negatively correlated with sea surface temperature, diminishing at a rate of 38% for every 1 °C increase. Although the temperature effect was strong, it did not explain all variability in parasite burden, suggesting that other factors may also have contributed to the long-term declines we observed. These data document one century of climate-associated parasite decline in Puget Sound—a massive loss of biodiversity, undetected until now.

Historical data are extremely rare but essential for ascertaining whether contemporary infectious disease burdens are unusual. Natural history collections are a valuable source of such data, especially for reconstructing long timelines of parasite abundance. We quantified the parasites of 109 museum specimens of English sole (Parophrys vetulus), an economically important flatfish, collected from Puget Sound, Washington, over a 90-year period (1930-2019). We counted nearly 2,500 individual parasites representing 23 distinct species/morphotypes and four broad taxonomic groupings. Of the 12 taxa that were prevalent enough to include in the analysis, nine did not change in abundance over time, two (an acanthocephalan and a trematode) decreased, and one (another trematode) increased. By broad taxonomic grouping, nematodes, trematodes, and leeches exhibited no change over time, whereas acanthocephalans declined significantly. The diverging patterns among parasite taxa suggest a double-edged sword of responses to long-term ocean change: some parasites might be on the rise, while others are declining.

Gongylonema archboldi n. sp. (Nematoda: Gongylonematidae) is described from tunnels in the gastric mucosa of the stomach of the cotton rat (Sigmodon hispidus) from Highlands County, Florida, U.S.A. Measurements are also given for specimens from cotton mice (Peromyscus gossypinus), oldfield mice (Peromyscus polionotus), Florida mice (Podomys floridanus), and golden mice (Ochrotomys nuttalli) from the same locality. Additional specimens were collected from the cotton rat and the rice rat (Oryzomys palustris) from Berry Island, San Patricio County, Texas. The new species is differentiated from congeners by a combination of the following characters: length of the left spicule, length and shape of the gubernaculum, distribution of cuticular bosses, length of esophagus, and distance of the vulva from the posterior end. The status of the genus Gongylonema in North American rodents is reviewed.

Many of the most contentious questions that concern the ecology of helminths could be resolved with data on helminth abundance over the past few decades or centuries, but unfortunately these data are rare. A new sub-discipline – the historical ecology of parasitism – is resurrecting long-term data on the abundance of parasites, an advancement facilitated by the use of biological natural history collections. Because the world's museums hold billions of suitable specimens collected over more than a century, these potential parasitological datasets are broad in scope and finely resolved in taxonomic, temporal and spatial dimensions. Here, we set out best practices for the extraction of parasitological information from natural history collections, including how to conceive of a project, how to select specimens, how to engage curators and receive permission for proposed projects, standard operating protocols for dissections and how to manage data. Our hope is that other helminthologists will use this paper as a reference to expand their own research programmes along the dimension of time.

Aim: While most free-living taxa follow the latitudinal diversity gradient (LDG), or the trend of higher diversity at lower latitudes, we know little about how the diversity of parasitic taxa is distributed across latitudes. To better understand the macroecological patterns of parasite diversity, we sought to determine whether (1) helminths follow the traditional LDG; (2) taxonomic resolution impacts observed patterns; (3) latitudinal patterns are consistent across levels of community organization and (4) helminth diversity is correlated with climate-and host-associated variables.

Abstract