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April 22, 2024

Breaking the cliché with South American spiders

A recent study on the coastal sand-dwelling spiders Allocosa senex and Allocosa marindia has challenged us to analyse the evolution of sexual dimorphism and behavioural patterns from new perspectives. Conversely to what is generally expected from spiders, these females of these species are the ones to search for mates and initiate courtship, while the males are larger than the females.

Atypical allocosinae?

Atypical patterns of dimorphism and sexual behaviour have been reported in a great variety of animals and have also been correlated to the species’ preferred environment. A. senex and A. marindia (both types of wolf spider) inhabit sandy beaches that suffer high temperature variations, strong winds, and strong habitat reduction and fragmentation. Our aim was to determine the factors that shape the origin and evolution of unexpected body and behavioural traits in these species. For that purpose, we needed to study other spiders of the same subfamily which inhabit different environments along South America.

Exploring South America

With a diverse group of researchers from Uruguay, Argentina, Brazil, Chile, and Catalonia, we performed field trips to locations along the coast of South America in search of Allocosinae spiders. We visited Lanín National Park (San Martín de los Andes, Argentina), Ischigualasto Provincial Park (Valley of the Moon, Argentina), El Palmar National Park on the banks of Uruguay River (Entre Ríos, Argentina), Río Clarillo National Park (Santiago Metropolitan Region, Chile), Pró-Mata Reserve (Rio Grande do Sul, Brazil), Parque das Dunas (Salvador de Bahía, Brazil), Protected Area Montes del Queguay (Paysandú, Uruguay), Melilla (Montevideo, Uruguay), and in the gardens of our own institute (yes, of the IIBCE!). Visiting each of these places, with different landscapes, was a unique experience.

We performed field trips during the summer and at night when these spiders are expected to be active. We collected the spiders found walking or at the entrance of their burrows (if they were burrowing species) and recorded the number of adults to estimate their nocturnal surface activity. At each sampling location, we recorded climatic variables and substrate characteristics. We also reviewed scientific collections of the California Academy of Sciences (United States), Butantan Institute (Brazil), Museum of Sciences and Technology of the Pontifical Catholic University of Rio Grande do Sul (Brazil), Argentine Museum of Natural Sciences (Argentina) and Faculty of Sciences (Uruguay). Once the individuals were identified, we measured the body size of males and females and compared them across sexes, habitats, species, and/or morphotypes (a group of different individuals of the same species in a population).

Revelations and a look into the future

We found that the subfamily Allocosinae presents greater diversity than what was previously known in South America, as well as discovering entirely new spider species. We reported new cases in which males are larger than females, where the species also inhabits coastal environments. One of these cases is the spider of the main image on this page that inhabits the volcanic sandy beaches of the Huechulafquen Lake, at Lanín National Park in Argentina. In this species, the males are much more active than females in contrast to the behavioural patterns of A. senex and A. marindia. On the other hand, not all the spiders associated with coastal sandy environments presented the atypical pattern described in A. senex and A. marindia. Finally, we confirmed that body size varied depending on the microenvironment, with Allocosinae spiders from grasslands and gardens being smaller than those from coastal environments.

Without a doubt, this project has been a before and after for many of those involved, not only because of the enormous load of data and questions generated but also due to all the memories treasured during those field trips that involved a scientific and cultural meeting of Ibero-American arachnology. There are still several key locations and countries to visit. Some examples are the Brazilian Amazonas, Parque Nacional Tayrona in Colombia, and the Galápagos Islands. We need to infer an updated phylogeny that allows us to map traits such as sexual size dimorphism and nocturnal mobility, considering the environments of each species, in order to search for patterns that allow tracing the origin and evolution of sexual traits in the subfamily Allocosinae.


Anita Aisenberg1 & Leticia Bidegaray-Batista2

1Departamento de Ecología y Biología Evolutiva, Centro de Investigación en Ciencias Ambientales, Instituto de Investigaciones Biológicas Clemente Estable, Uruguay
2Departamento de Biodiversidad y Genética, Centro de Investigación en Ciencias Ambientales, Instituto de Investigaciones Biológicas Clemente Estable, Uruguay

Based on the study published as:

Aisenberg A, Bollatti F, Oviedo-Diego M, Albín A, Alves Días M, Arnedo MA, Bréscovit AD, Casacuberta M, Cavassa D, Gonnet V, Izquierdo M, Laborda Á, Piacentini LN, Pliscoff P, Postiglioni R, Simó M, Texeira RA, Bidegaray-Batista L (2023) Breaking the cliché: Sex reversal in size dimorphism and mobility in South American Allocosinae (Lycosidae) spiders. Biological Journal of the Linnean Society, 140(2), 224-239.


Aisenberg, A, et al (2014) Adventurous females and demanding males: sex role reversal in a neotropical spider. In: Sexual Selection: Perspectives and Models from the Neotropics (Macedo RH & Machado G, eds). USA: Elsevier, pp. 163-182.

Aisenberg A, et al (2023) Breaking the cliché: Sex reversal in size dimorphism and mobility in South American Allocosinae (Lycosidae) spiders. Biological Journal of the Linnean Society, 140(2), 224-239.

Bidegaray-Batista L, et al, (2017) Dispersal strategies, genetic diversity and distribution of two wolf spiders (Araneae, Lycosidae), potential bio-indicators of ecosystem health of coastal dune habitats of South America. In: Behavioral and Ecology of Neotropical Spiders - Contributions of studies from the Neotropical region (Viera C & Gonzaga MO, eds). Cham, Switzerland: Springer, pp. 109-135.

Written By

Anita Aisenberg
Instituto de Investigaciones Biológicas Clemente Estable

Contact Details

Email: [email protected]

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