Oomycete parasites in freshwater copepods of Patagonia: effects on survival and recruitment

Abstract

Copepods are hosts to various oomycete parasite species, but the effects of pathogens on copepod populations have rarely been studied. This study aimed to characterize oomycete infection in the freshwater copepod Parabroteas sarsi in a temporary pond in Patagonia (Argentina). A complete hydroperiod was monitored, evaluating environmental variables as influencing factors in the oomycete infections. Laboratory experiments were performed to evaluate the susceptibility of infected copepods to consumption by predators. Although 5 species of copepods were present in the pond, only ovigerous P. sarsi females were parasitized by oomycetes. Two species of oomycetes were always found together: Aphanomyces ovidestruens and Pythium flevoense. Infections were detected at water temperatures >20°C, with a positive relationship between temperature and parasite prevalence. Infection occurred after a decrease in large filter-feeder densities. The pathogens were not lethal to P. sarsi females in the short-term, but did produce mortality of entire egg sacs, thus negatively impacting subsequent recruitment. Mean prevalence of infection in females was 53%, reaching 83% in December. Females have the capacity to release an infected egg sac and generate a new one in a few days. This infection does not affect the susceptibility of P. sarsi to the predator Notonecta vereertbruggheni. The decrease in female abundance registered towards the end of the hydroperiod could be related to a combination of factors that may have a differential effect on female survival, such as increasing temperature, the energy cost of egg sac development and carrying and oomycete infection.

Hot and sick? Impacts of warming and a parasite on the dominant zooplankter of Lake Baikal

“…Since we did not quantify the number of eggs per egg sack, only the number of hatched nauplii, we are unsure whether this effect was a result of increased number of eggs per egg sack from Saprolegnia ‐exposed mothers or of lower egg mortality rates. The increased fecundity of Saprolegnia ‐exposed females is especially surprising since all previously described oomycetes infecting freshwater copepods are brood parasites that destroy egg sacks and reduce reproductive output (Redfield and Vincent 1979; Burns 1989; Miao and Nauwerck 1999; Valois and Burns 2016; Garcia et al 2018). One possible explanation for the increased reproductive output of Saprolegnia ‐exposed E. baikalensis individuals is compensation by infected mothers for their infection‐associated shorter life span, an idea known as the “terminal investment hypothesis” or “fecundity compensation” (Minchella and Loverde 1981; Velando et al 2006; Vale and Little 2012; Brannelly et al 2016).…”

“…Warming temperatures may also affect copepods such as E. baikalensis through increasing impact of parasites at higher temperatures (e.g., Miao and Nauwerck 1999; Garcia et al 2018). As early as 1926, Lake Baikal researchers documented occasional mass epizootics of a fungal parasite, putatively identified as Saprolegnia sp.…”

Record of parasitic oomycetes on neotropical copepods in aquatic environments of Northwestern Patagonia (Argentina)

“…in freshwater copepods. Garcia et al (2018) through laboratory experiments have shown that oomycetes are not lethal to females in the short-term and do not affect their susceptibility to insect predation. However, the proportion of females decreased after the spread of the infection, when the daily water temperature increased above 20 °C.…”

“…High temperatures can accelerate metabolism and oxygen consumption, leading to excessive use of protein and a low survival rate (Li et al, 2009;Garcia & Diéguez, 2014). It is possible that a combination of these factors imposes severe restraints on P. sarsi females from spring onwards, differentially affecting their survival (Garcia et al, 2018). However, little is known regarding this aspect and further investigation is required on the subject.…”

“…Oomycetes species found on freshwater copepods belong to the genera Aphanomyces, Saprolegnia (order Saprolegniales), Pythium and Lagenidium (order Pythiales) (Valois & Poulin, 2015). Currently, only four copepods genera have reported oomycetes infections: Boeckella in New Zealand (Burns, 1985a), Leptodiaptomus in North America (Redfield & Vincent, 1979), Eudiaptomus in Europe (Rossetti, 2005) and Parabroteas in South America (Garcia et al, 2018).…”