The contrasting hidden consequences of parasitism: Effects of a hematophagous nematode (Uncinaria sp.) in the development of a marine mammal swimming behavior

Mitigating disease risk in an endangered pinniped: early hookworm elimination optimizes the growth and health of Australian sea lion pups

The Australian sea lion (Neophoca cinerea) experiences high pup mortality of seasonally alternating severity, partly attributed to endemic hookworm (Uncinaria sanguinis) infection. To further explore health outcomes of early hookworm elimination, a treatment trial was conducted at Seal Bay Conservation Park, South Australia, over consecutive lower and higher mortality breeding seasons (2019, 19.2%; 2020-1; 28.9%). Pups (n = 322) were stratified into two age cohorts (median 14 d and 24 d recruitment ages) and randomly assigned to treated (topical ivermectin 500  μg/kg) or control (untreated) groups. A younger prepatent cohort <14 d old (median 10 d) was identified a posteriori. A seasonally independent growth benefit resulted from hookworm elimination across all age cohorts. The greatest relative improvements (bodyweight + 34.2%, standard length + 42.1%; p ≤ 0.001) occurred in the month post-treatment, in the youngest prepatent cohort. A significant benefit of lesser magnitude (bodyweight + 8.6-11.6%, standard length + 9.5-18.4%; p ≤ 0.033) persisted up to 3  months across all age cohorts - greatest in the youngest pups. Treatment resulted in immediate improvement in hematological measures of health - decreased anemia and inflammation severity (p ≤ 0.012). These results enhance our understanding of host-parasite-environment interactions within the context of hematological ontogenesis, confirm the seasonally independent benefits of hookworm disease intervention, and further inform conservation recommendations for this endangered species.

Using Next-Generation Sequencing to Disentangle the Diet and Incidence of Intestinal Parasites of Falkland Flightless Steamer Duck Tachyeres brachypterus and Patagonian Crested Duck Lophonetta specularioides Sharing a South Atlantic Island

Species overlapping in habitat use can cohabit depending on how they exploit resources. To understand segregation in resource use, an exhaustive knowledge of the diet is required. We aimed to disentangle the diet composition of the Falkland Flightless Steamer Duck Tachyeres brachypterus and the Patagonian Crested Duck Lophonetta specularioides sharing a coastal environment. Using DNA extracted from scats and Illumina sequencing, we generated a list of molecular operational taxonomic units. Both ducks consumed a variety of invertebrates, frequently overlapping in the taxa consumed. However, only the Falkland Flightless Steamer Ducks consumed fish, which might be indicative of dietary specialization and inter-specific segregation in the restricted space that these birds share. Moreover, the female and male Falkland Flightless Steamer Ducks consumed different fish prey, with almost one-third of the fish taxa being consumed by females only and another similar number consumed by males only. This result might suggest a case of intra-specific competition, triggering sexual segregation. Additionally, we detected parasitic Platyelminthes (Cestoda and Trematoda), with different frequencies of occurrence, probably related to the different diet compositions of the ducks. This study provides the necessary baseline for future investigations of the ecological segregation of these ducks.

The energetic costs of sub-lethal helminth parasites in mammals: a meta-analysis

Parasites, by definition, have a negative effect on their host. However, in wild mammal health and conservation research, sub-lethal infections are commonly assumed to have negligible health effects unless parasites are present in overwhelming numbers. Here, we propose a definition for host health in mammals that includes sub-lethal effects of parasites on the host's capacity to adapt to the environment and maintain homeostasis. We synthesized the growing number of studies on helminth parasites in mammals to assess evidence for the relative magnitude of sub-lethal effects of infection across mammal taxa based on this expanded definition. Specifically, we develop and apply a framework for organizing disparate metrics of parasite effects on host health and body condition according to their impact on an animal's energetic condition, defined as the energetic burden of pathogens on host physiological and behavioural functions that relate directly to fitness. Applying this framework within a global meta-analysis of helminth parasites in wild, laboratory and domestic mammal hosts produced 142 peer-reviewed studies documenting 599 infection-condition effects. Analysing these data within a multiple working hypotheses framework allowed us to evaluate the relative weighted contribution of methodological (study design, sampling protocol, parasite quantification methods) and biological (phylogenetic relationships and host/parasite life history) moderators to variation in the magnitude of health effects. We found consistently strong negative effects of infection on host energetic condition across taxonomic groups, with unusually low heterogeneity in effect sizes when compared with other ecological meta-analyses. Observed effect size was significantly lower within cross-sectional studies (i.e. observational studies that investigated a sub-set of a population at a single point in time), the most prevalent methodology. Furthermore, opportunistic sampling led to a weaker negative effect compared to proactive sampling. In the model of host taxonomic group, the effect of infection on energetic condition in carnivores was not significant. However, when sampling method was included, it explained substantial inter-study variance; proactive sampling showing a strongly significant negative effect while opportunistic sampling detected only a weak, non-significant effect. This may partly underlie previous assumptions that sub-lethal parasites do not have significant effects on host health. We recommend future studies adopt energetic condition as the framework for assessing parasite effects on wildlife health and provide guidelines for the selection of research protocols, health proxies, and relating infection to fitness.

Shifts in maternal foraging strategies during pregnancy promote offspring health and survival in a marine top predator

The success of maternal foraging strategies during the rearing period can greatly impact the physiology and survival of dependent offspring. Surprisingly though, little is known on the fitness consequences of foraging strategies during the foetal period. In this study, we characterized variation in maternal foraging strategy throughout pregnancy in a marine top predator (South American fur seal, Arctocephalus australis), and asked if these shifts predicted neonatal health and postnatal survival. We found that during early pregnancy all pregnant females belonged to a single, homogenized foraging niche without evident clusters. Intriguingly though, during late pregnancy, individual fur seal mothers diverged into two distinct foraging niches characterized by a benthic-nearshore and a pelagic-offshore strategy. Females that shifted towards the benthic-nearshore strategy gave birth to pups with greater body mass, higher plasmatic levels of glucose and lower levels of blood urea nitrogen. The pups born to these benthic females were eight times more likely to survive compared to females using the pelagic-offshore foraging strategy during late pregnancy. These survival effects were mediated primarily by the impact of foraging strategies on neonatal glucose independent of protein metabolic profile and body mass. Benthic-nearshore foraging strategies during late pregnancy potentially allow for the greater maternal transfer of glucose to the foetus, leading to higher chances of neonatal survival. These results call for a deeper understanding of the balance between resource acquisition and allocation provided by distinct foraging polymorphisms during critical life-history periods, and how this trade-off may be adaptive under certain environmental conditions.

Lower marine productivity increases agonistic interactions between sea lions and fur seals in Northern Pacific Patagonia

Interspecific interactions are key drivers of individual and population-level fitness in a wide range of animals. However, in marine ecosystems, it is relatively unknown which biotic and abiotic factors impact behavioral interactions between competing species. We assessed the impact of weather, marine productivity, and population structure on the behavioral agonistic interactions between South American fur seals (SAFSs), Arctocephalus australis, and South American sea lions (SASLs), Otaria byronia, in a breeding colony of SAFS. We hypothesized that agonistic interactions between SAFSs and SASLs respond to biotic and abiotic factors such as SAFS population structure, marine productivity, and weather. We found that SASL and SAFS interactions almost always resulted in negative impacts on the social structure or reproductive success of the SAFS colony. SASL adult males initiated stampedes of SAFS and/or abducted and predated SAFS pups. Adult SAFS males abundance and severe weather events were negatively correlated with agonistic interactions between species. However, proxies for lower marine productivity such as higher sea surface temperature and lower catches of demerso-pelagic fish were the most important predictors of more frequent agonistic interactions between SAFS and SASL. Under the current scenario of decline in marine biomass due to global climate change and overfishing, agonistic interactions between competing marine predators could increase and exacerbate the negative impacts of environmental change in these species.

Topical ivermectin is a highly effective seal 'spot-on': A randomised trial of hookworm and lice treatment in the endangered Australian sea lion (Neophoca cinerea)

The Australian sea lion (Neophoca cinerea) is an endangered and declining otariid species, with a high rate of pup mortality associated with endemic hookworm (Uncinaria sanguinis) infection a suspected contributor to this decline. Injected ivermectin is an effective treatment for Uncinaria sp. in otariids, with optimal outcomes achieved by the early treatment of pups prior to disease development. This randomised controlled trial evaluated the effectiveness of the novel use of a topical ivermectin formulation against hookworm infection and lice (Antarctophthirus microchir) infestation, in comparison with injected ivermectin. During the 2017 breeding season at Dangerous Reef, South Australia, pups ≤ 70 cm in standard length (≤ 2 weeks of age; n = 85) were randomised to single dose topical (500 μg/kg spot-on; n = 27) or injected (200 μg/kg subcutaneous; n = 29) ivermectin treatment groups, or to an untreated control group (n = 29). Topical ivermectin was highly effective for U. sanguinis elimination, and not significantly different to the injected formulation (estimated effectiveness 96.4% and 96.8%, respectively; P > 0.05). Its application resulted in an 81.6% reduction and 62.7% additional clearance for A. microchir infestation by 15-24 days post-treatment, compared with untreated control pups (also not significantly different to injected ivermectin; 83.1% and 59.4%, respectively; P > 0.05). Treatment with either ivermectin formulation significantly ameliorated increases in inflammatory markers detected in the blood of untreated control pups - peripheral blood eosinophil counts (persisting to 36-41 days post-recruitment P < 0.05) and increased plasma protein concentrations (15-24 days post-recruitment; P < 0.05). Further, an initial short-term decrease in body condition in the control group was not observed in either of the treatment groups. This study demonstrates that topical ivermectin is an effective antiparasitic treatment in N. cinerea. It offers an alternative administration method for ivermectin delivery to a young pup cohort in this species, and an alternative, minimally invasive management tool for species conservation.

GEOGRAPHICAL VARIATION OF ENTEROPARASITISM IN THE SOUTHERN SEA LION OTARIA FLAVESCENS (SHAW, 1800) OFF THE COAST OF CHILE AS EVIDENCED WITH COPROLOGICAL TESTS: IMPLICATONS FOR ZOONOTIC RISKS

The scarce information on the helminth fauna in otariids from the Southeastern Pacific comes mainly from stranded individuals or killed for that purpose. In this study, we compared the abundance and composition of enteroparasitic assemblages of Otaria flavescens using coprological techniques. Three sampling localities from north to south spanning 2,200 km off the Chilean coast were considered (Iquique, Viña del Mar, and Talcahuano). In all, 60 fecal samples were collected, and eggs belonging to 5 taxa were found in 91.6% of the samples. They were the anisakid nematodes Contracaecum and Pseudoterranova, the cestode Adenocephalus (syn. Diphyllobothrium), the trematode Ogmogaster, and the acanthocephalan Corynosoma. Samples from southern Chile (Talcahuano) showed the highest prevalence. Adenocephalus eggs had the highest prevalence and abundance in Iquique and Talcahuano, whereas Ogmogaster was the less prevalent and abundant in all sampling localities. Corynosoma eggs had similar prevalence and abundance among sampling localities, and Pseudoterranova eggs were absent in Iquique and with median prevalence values in Viña del Mar and Talcahuano. Thus, the composition of parasite egg assemblages was different between sampling localities. These differences between sampling localities may help to explain differential records of some zoonotic parasitoses such as pseudoterranovosis and diphyllobothriosis in Peru and Chile, where consumption of raw or marinated fish (ceviche) is common. For example, the lower diversity of parasite egg assemblages in the northern Chilean coast may be due to the absence or lower abundance of first intermediate/paratenic hosts of Pseudoterranova.

Novel infections of Corynosoma enhydri and Profilicollis sp. (Acanthocephala: Polymorphidae) identified in sea otters Enhydra lutris

Infectious disease is a major cause of mortality for sea otters Enhydra lutris, a keystone species of continued concern for conservationists. Parasitic infection has long been identified as a cause of mortality in otters in both Alaska and California, USA. Corynosoma enhydri (Acanthocephala) is the only parasite that uses sea otters as its primary definitive host and is highly prevalent in otter populations; however, it is generally considered unimportant both pathologically and ecologically, although this assumption is based on limited empirical knowledge. Research has instead focused on Profilicollis infections (P. major, P. kenti, P. altmani) as a significant source of otter mortality due to associated enteritis and peritonitis, which are threats to otter health. Here we describe acanthocephalan infections in sea otters by Profilicollis spp. and C. enhydri, from a survey comparing C. enhydri infections between northern sea otters E. lutris kenyoni (n = 12) and southern sea otters E. lutris nereis (n = 19). We report a novel infection of C. enhydri in a pup approximately 1 mo of age, which shows that the early introduction to solid food at around 3 wk by their mothers may lead to subsequent infection via infected prey items. We also document the first 2 known cases of Profilicollis infection in northern sea otters, which may present an unknown threat to the Alaskan population, or may be an interesting example of accidental infection.