Parasitism in Gambusia affinis: Fitness Effects in an Incipient Matrotroph

Parasitism in viviparous vertebrates: an overview

The reproductive mode of viviparity has independently evolved in various animal taxa. It refers to the condition in which the embryos or young develop inside the female's body during gestation, providing advantages such as protection, nutrition, and improved survival chances. However, parasites and diseases can be an evolutionary force that limit the host's resources, leading to physiological, morphological, and behavioral changes that impose additional costs on both the pregnant female and her offspring. This review integrates the primary literature published between 1980 and 2021 on the parasitism of viviparous hosts. We describe aspects such as reproductive investment in females, offspring sex ratios, lactation investment in mammals, alterations in birth intervals, current reproductive investment, variations between environments, immune system activity in response to immunological challenges, and other factors that can influence the interaction between viviparous females and parasites. Maintaining pregnancy incurs costs in managing the mother's resources and regulating the immune system's responses to the offspring, while simultaneously maintaining an adequate defense against parasites and pathogens. Parasites can significantly influence this reproductive mode: parasitized females adjust their investment in survival and reproduction based on their life history, environmental factors, and the diversity of encountered parasites.

An Unusual Type of Neoechinorhynchus cylindratus (Acanthocephala: Neoechinorhynchidae) from Gambusia affinis in Peru, with Notes on Introductions

BACKGROUND

Neoechinorhynchus cylindratus Van Cleave (Zoo Anz 43: 177-1990, 1913) Van Cleave (Ill Natl Hist Surv Bull 13:225-257, 1919) is a North American acanthocephalan originally described from Micropterus salmoides (Lacépède) in Pelican Lake, Minnesota. It is common in Centrarchids but also not infrequent in fishes of other families.

PURPOSE

A unique population of N. cylindratus was discovered in Peru. It needed to be described and its introduction into Peru investigated.

METHODS

Standard processing of specimens and staining in Borax carmine and fast green for creating whole mounts were employed. Literature sources were available from the OMA personal collection.

RESULTS

The descriptive accounts of N. cylindratus have been rather stable over the years since its original description. It has been, however, oddly identified from Gambusia affinis (Baird and Girard) in Peru. Females of the Peruvian specimens were, however, not typical in having a terminal-near terminal gonopore at odds with the sub-ventral position characteristic of the usual populations of N. cylindratus in North America. We describe the Peruvian material and outline the distinct morphological variations from the North American populations in the position of the female gonopore, among other characters. We also explain its introduction into Peru and the translocation of the position of female gonopore to the terminal position.

CONCLUSIONS

The translocation to the terminal position of the female gonopore in the Peruvian material is attributed to host related developmental factors. The route of introduction of N. cylindratus into Peru through the introduction of G. affinis from the United States has been accounted for. It may be comparable to the introduction of the same acanthocephalan species into northern Mexico via the documented introduction of its primary host, M. salmoides, also from the United States into Mexico in 1930. The introduction of Acanthocephalus dirus Van Cleave (Ill Natl Hist Surv Bull 13:225-257, 1919) (Van Cleave and Townsend, 1936) into Mexico is also discussed.