Litter size and seasonality in reproduction for Guianan rodents and opossums

ABSTRACT

We studied the litter sizes of small rodents and opossums caught in the Guianan Region (Brazilian Amapá, French Guiana, Suriname, and Guyana) by pooling the data of animals collected during various field trips conducted primarily between 1990 and 2017. A series of 569 counts of embryos (or of pouch young for marsupials) in 40 species of Didelphidae (N = 12 species), Sigmodontinae (18), Murinae (2), and Echimyidae (8) allowed for a more detailed characterization of the reproductive condition of 14 species known each by more than 10 pregnant females. For eight species with at least 20 pregnant females, an examination of seasonality in breeding occurrence documented that the two months with the lowest percentage of pregnant females are July and August (16.0 and 17.3%, respectively) during the end of the long wet season and beginning of the dry season. By contrast, January and February showed the highest abundance of pregnancies (57.9% and 55.8%, respectively) during the beginning of the long wet season. This timing coincides with most juveniles foraging during the height of the wet season in May when food is presumably most prevalent.

RESUMO

Nós estudamos o tamanho das ninhadas de pequenos roedores e marsupiais capturados na Região Guiana (Amapá – Brasil, Guiana Francesa, Suriname e Guiana) reunindo dados coletados em diversas campanhas de campo conduzidas entre os anos de 1990 e 2017. Obtivemos resultados de 569 fêmeas com embriões (ou com filhotes na bolsa para marsupiais) de 40 espécies, das famílias Didelphidae (N = 12 espécies), Sigmodontinae (N=18), Murinae (N=2) e Echimyidae (N=8). Para 14 espécies com mais de 10 fêmeas grávidas foi possível a caracterização da condição reprodutiva. Para oito espécies, com pelo menos 20 registros de fêmeas grávidas, foi possível examinar sazonalidade na ocorrência de reprodução. Os dois meses com a menor porcentagem de grávidas foram julho e agosto (16,0 e 17,3% respectivamente) no final da longa estação chuvosa e início da estação seca. Por outro lado, janeiro e fevereiro mostraram a maior abundância de grávidas (57,9% e 55,8%, respectivamente) durante o início da longa estação chuvosa. Este momento coincide com a maioria dos juvenis forrageando durante o auge da estação chuvosa em maio quando ocorre, presumivelmente, maior disponibilidade de alimentos.

KEYWORDS:

• Seasonality
• reproduction
• litter size
• Guyana
• French Guiana

Acknowledgments

Our warmest thanks to all collectors who either joined us in the field and/or donated to us their biological materials for curating. We acknowledge the help of Benoit de Thoisy and Jean-François M. Mauffrey in French Guiana, the Environmental Protection Agency in Guyana, the Nature Conservation Division in Suriname, the Direction Régionale de l’Environnement, de l’Aménagement, et du Logement in French Guiana, and Elizandra Matos Cardoso, Keliane Cruz Castro and Silvia Helena de Oliveira in Brazil.

Disclosure statement

No potential conflict of interest was reported by the authors.

Supplemental material

Supplementary data can be accessed here.

Additional information

Funding

This work has benefited from an “Investissements d’Avenir” grant managed by the French Agence Nationale de la Recherche [CEBA, ref. ANR-10-LABX-25-01].