Cause Of Juvenile Mortality Research Articles

Testing microbial pathogens as a cause of early juvenile mortality in wild populations of benthic invertebrates

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 562:53-63 (2016) - DOI: https://doi.org/10.3354/meps11975 Testing microbial pathogens as a cause of early juvenile mortality in wild populations of benthic invertebrates Samantha D. Sandee, Jonathan D. Van Hamme, Louis A. Gosselin* Department of Biological Sciences, Thompson Rivers University, 900 McGill Road, Kamloops, BC V2C 0C8, Canada *Corresponding author: lgosselin@tru.ca ABSTRACT: Microbial pathogens such as bacteria, viruses, fungi, and protozoa are potentially important causes of mortality during the critical first days of juvenile life in benthic invertebrates, but their effect on early juveniles in natural habitats remains unexplored. We therefore placed newly-settled mussels (Mytilus trossulus) and barnacles (Balanus glandula, Chthamalus dalli), and newly-hatched snails (Nucella ostrina) in screened cages submerged in the field, exposing them to ambient microbial organisms while isolating them from most non-microbial mortality factors. Mortality over a 5 d period was only 0-3% in M. trossulus and N. ostrina and 0-10% in B. glandula and C. dalli. Mortality was consistent among replicate trials in the same summer and between 2 different years, and was much lower than previously reported natural early juvenile mortality in these species. We then examined whether bacterial infection caused the few juvenile deaths in our field experiment. Dosage testing in the laboratory with 5 antibiotics resulted in an antibiotic cocktail providing broad-spectrum antibacterial protection without affecting the health of juveniles. In a second field experiment, early juvenile M. trossulus and N. ostrina exposed to the antibiotic cocktail 3 times daily did not experience reduced mortality relative to controls. Our findings suggest that, at least in some species, microbial pathogens are not a direct cause of juvenile mortality in the field, thus narrowing the list of potential causes of early juvenile mortality to the non-microbial factors excluded from our experiments. KEY WORDS: Early benthic phase · Natural mortality · Bacteria · Viruses · Antibiotics · Immune response · Survivorship · Mussels · Barnacle cyprids · Snails Full text in pdf format PreviousNextCite this article as: Sandee SD, Van Hamme JD, Gosselin LA (2016) Testing microbial pathogens as a cause of early juvenile mortality in wild populations of benthic invertebrates. Mar Ecol Prog Ser 562:53-63. https://doi.org/10.3354/meps11975 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 562. Online publication date: December 29, 2016 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2016 Inter-Research.

The challenges of the first migration: movement and behaviour of juvenile vs. adult white storks with insights regarding juvenile mortality.

Migration conveys an immense challenge, especially for juvenile birds coping with enduring and risky journeys shortly after fledging. Accordingly, juveniles exhibit considerably lower survival rates compared to adults, particularly during migration. Juvenile white storks (Ciconia ciconia), which are known to rely on adults during their first fall migration presumably for navigational purposes, also display much lower annual survival than adults. Using detailed GPS and body acceleration data, we examined the patterns and potential causes of age-related differences in fall migration properties of white storks by comparing first-year juveniles and adults. We compared juvenile and adult parameters of movement, behaviour and energy expenditure (estimated from overall dynamic body acceleration) and placed this in the context of the juveniles' lower survival rate. Juveniles used flapping flight vs. soaring flight 23% more than adults and were estimated to expend 14% more energy during flight. Juveniles did not compensate for their higher flight costs by increased refuelling or resting during migration. When juveniles and adults migrated together in the same flock, the juvenile flew mostly behind the adult and was left behind when they separated. Juveniles showed greater improvement in flight efficiency throughout migration compared to adults which appears crucial because juveniles exhibiting higher flight costs suffered increased mortality. Our findings demonstrate the conflict between the juveniles' inferior flight skills and their urge to keep up with mixed adult-juvenile flocks. We suggest that increased flight costs are an important proximate cause of juvenile mortality in white storks and likely in other soaring migrants and that natural selection is operating on juvenile variation in flight efficiency.

Conservation status and reproduction of the critically endangered freshwater pearl mussel (Margaritifera margaritifera) in Northern Ireland

ABSTRACTFreshwater unionoids are one of the most threatened animal groups worldwide and the freshwater pearl mussel Margaritifera margaritifera is currently listed as critically endangered in Europe. The EC Habitats Directive requires that EU Member States monitor the distribution and abundance of this species and report regularly on its conservation status.The pearl mussel meta‐population in Northern Ireland was surveyed to assess temporal population trends in Special Areas of Conservation (SACs) and mussel reproduction throughout its range.Mussels occurred in six rivers and numbers within three SAC designated sites remained stable between 2004–2007 and 2011. The discovery of more than 8000 previously unknown individuals in the Owenreagh River contributed to an overall increase (+56.8%) in the total known population. All populations actively reproduced during 2010 with approximately half of all individuals gravid. Moreover, suitable salmonid hosts occurred at all sites with 10.7% of salmon and 22.8% of trout carrying encysted glochidia. Populations were composed entirely of aged individuals with little evidence of recent recruitment.It is inferred that the break in the life cycle must occur during the juvenile stage when glochidia metamorphose and settle into the interstitial spaces within the substrate. Water quality parameters, most notably levels of suspended solids, exceeded the recommended maximum thresholds in all rivers.It is posited that the deposition of silt may be the main cause of juvenile mortality contributing to a lack of recruitment. Consequently, all populations were judged to be in ‘unfavourable’ conservation status. Catchment‐level management plans are urgently needed to reduce siltation with the aim of improving recruitment. These results have implications for the success of ex situ conservation programmes; specifically, the size at which captive‐bred juveniles are released into the wild. Further research is required to assess the vulnerabilities of early life‐stages of M. margaritifera to siltation. Copyright © 2012 John Wiley & Sons, Ltd.

When Good Fish Make Bad Decisions: Coho Salmon in an Ecological Trap

AbstractCoho salmon Oncorhynchus kisutch are a threatened species in California. In the Shasta River, they may be caught in an ecological trap that is exacerbating their decline. Adults appear to have equal preferences for spawning habitat that reduces the survival of their young and that of apparently similar quality where survival would be more likely. The primary cause of juvenile mortality is water withdrawals, which degrade summer water quality and create barriers to movement to habitats with more suitable rearing conditions. The situation has been exacerbated by the addition of gravel to support spawning fall‐run Chinook salmon O. tshawytscha, creating habitat that is also attractive to spawning coho salmon in locations where juvenile coho salmon survival will be extremely low. The Shasta River acts as a conceptual model of how habitat degradation and ecologically naive restoration actions may combine to create severe ecological traps for nontarget species.Received March 10, 2011; accepted October 11, 2011

Ontogenetic shift in susceptibility to predators in juvenile northern abalone, Haliotis kamtschatkana

Predation has been suggested as a major cause of juvenile mortality in benthic marine invertebrates. However, the extent to which juveniles are susceptible to predators is unknown for most species, and it remains unclear to what extent ontogenetic shifts in susceptibility to predators are common among marine invertebrates. This study examined the northern abalone Haliotis kamtschatkana, a species listed as threatened in British Columbia, Canada. Our goals were to characterize the diversity and abundance of species that prey on juvenile abalone and determine if abalone experience an ontogenetic shift in susceptibility to predators. Juvenile H. kamtschatkana were found to be susceptible to a broad variety of predators: 14 of the 37 potential predator species to which we offered juvenile abalone (≤ 28 mm shell length (SL)) consumed at least one juvenile abalone. Four of those species (three crabs and one seastar) consumed ≥ 10% of the juvenile abalone that were offered in the laboratory. These species were present at field sites where abalone are found, indicating that they have the potential to be significant predators of juvenile H. kamtschatkana in the wild. The most abundant predators were small crabs, especially Lophopanopeus bellus (black-clawed crabs) and Scyra acutifrons (sharp-nosed crabs). Juvenile H. kamtschatkana also experienced a pronounced ontogenetic shift in susceptibility to predators. The risk of predation for juvenile H. kamtschatkana decreased rapidly with increasing body size, especially over the 12–13 mm SL size range. Susceptibility remained low beyond 13 mm SL, indicating relatively low and unchanging levels of predation risk once the individual reaches this size. Although abalone are susceptible to several species during the first 1–2 years of life, predator effects on juvenile abalone abundance and microhabitat use may largely be attributable to the influence of only 1 or 2 predator species that can only kill abalone < 13 mm SL.

The role of intraspecific predation in the survival of juvenile wolverines Gulo gulo

Wolverine Gulo gulo populations have a low reproductive potential and are thus relatively sensitive to changes in survival rates. Consequently, knowledge about survival and mortality causes in juvenile wolverines is important for a sound management of the species. We estimated survival rates for juvenile wolverines and evaluated the relative importance of intraspecific predation compared to other mortality causes in northern Scandinavia during 1993–2001. We monitored 80 radio‐marked juvenile wolverines from May to February. Intraspecific predation was the most important cause of juvenile mortality and occurred during two periods. First, seven juveniles were killed in May‐June when still altricial, i.e. infanticide. Second, four juvenile females were killed by conspecifics outside their mothers' territories after independence in August–September. The survival rate of radio‐marked juveniles during May‐February was 0.68. There was a strong tendency for survival to be lower during the summer when juveniles were altricial, than after they became independent. The estimates of survival rates and mortality causes provided by this study are important for the understanding of wolverine population dynamics. Currently, our data are too weak to suggest an explicit explanation for infanticide in spring/early summer. Still, in the light of the available information on wolverine life history and infanticide patterns in other species, we suggest two, not mutually exclusive, hypotheses to consider for further investigation: 1) males kill non‐related juveniles to increase their reproductive success, and 2) females kill non‐related juveniles to reduce competition for resources. In addition, attention should be given to the alternative hypothesis that infanticide in wolverines is non‐adaptive. Finally, we suggest that independent juvenile females were killed by resident females in territorial defence.

Characteristics and pathogenicity of a novel herpesvirus isolated from adult and subadult white sturgeon Acipenser transmontanus

DAO Diseases of Aquatic Organisms Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials DAO 22:199-210 (1995) - doi:10.3354/dao022199 Characteristics and pathogenicity of a novel herpesvirus isolated from adult and subadult white sturgeon Acipensertransmontanus Watson LR, Yun SC, Groff JM, Hedrick RP A syncytium-inducing viral agent was initially isolated from the ovarian fluid of a domestic white sturgeon Acipensertransmontanus female using the sturgeon spleen cell line WSS-2. Examination of infected cells by transmission electron microscopy revealed ultrastructural characteristics typical of the Herpesviridae. On the basis of differences shown by comparative invitro growth studies and serological assays, the new adult isolate was tentatively designated WSHV-2 to distinguish it from a previously reported herpesvirus from juvenile white sturgeon, WSHV (WSHV-1). A water-borne transmission trial at 3 virus concentrations was conducted to determine the susceptibility of juvenile sturgeon to the newly isolated virus. At virus doses of 105 and 104 TCID50 ml-1 cumulative mortality reached 80% within 6 wk at a water temperature of 17*C. Virus was reisolated from all mortalities with concentrations approaching 107 TCID50 g-1 in cutaneous epithelial tissues where severe hyperplastic lesions were observed. Challenge with 103 TCID50 ml-1 of WSHV-2 failed to induce clinical signs or mortality, although chronic subclinical infections were detected in a majority of survivors 70 d post-challenge. During our investigations of WSHV-2 from adult sturgeon, a second virus isolation was obtained from ulcerative skin lesions of naturally infected subadult white sturgeon. This virus induced identical cytopathic effects in WSS-2 cells to that caused by the adult isolate from ovarian fluid. Serum anti-WSHV-2 neutralizing activity was detected in subadults with skin lesions and among fish recovering from these lesions. Serum from naturally-infected juveniles and serum from adults hyperimmunized with the WSHV-2 from the ovarian fluid were used to compare the adult and subadult viruses. The 2 agents were neutralized with these 2 sera which conversely failed to neutralize WSHV-1 at the lowest dilution tested. Our studies demonstrate that at least 2 pathogenic herpesviruses are found among white sturgeon. The newly recognized WSHV-2 can cause both acute and chronic infections and possibly a latent carrier state in white sturgeon. WSHV-2 is the fourth virus to be observed as a cause of juvenile mortality among intensively reared white sturgeon populations. Herpesvirus . Skin lesion . Sturgeon Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in DAO Vol. 22, No. 3. Publication date: July 13, 1995 Print ISSN:0177-5103; Online ISSN:1616-1580 Copyright © 1995 Inter-Research.

Early Survival of Juvenile Snowshoe Hares

Juvenile snowshoe hares (Lepus americanus) were radio—tagged at birth on one food addition grid and one control grid, to determine early juvenile survival, the effects of the food addition on survival, and proximate causes of mortality. Indices of survival were also estimated by live—trapping on these grids and on a replicate pair of grids. The overall 30—d survival rates of radio—tagged leverets were 0.46, 0.15, and 0.43 for the first, second, and third litters of the year, respectively. There were no differences between early juvenile survival on the food addition and control grids in any of the litter groups. The main proximate cause of juvenile mortality was predation by small mammalian predators, the most important being red squirrels and arctic ground squirrels. Seventy percent of early juvenile mortality occurred during the first 5 d after birth. Survival of littermates was not independent; litters tended to all live or die as a unit more often than expected by chance. Fifty—one percent of litters had no known survivors after 14 d of age. Individual survival rates were negatively related to litter size and positively related to body size at birth, and litter size was negatively correlated with body size. These correlations were most closely related to differences in life history traits among litters born at different times of the summer, rather than to trade—offs among traits within litter groups.

Contemporary Threats to Adolescent Health in the United States

Over the past 30 years, adolescents have been the only population in the United States who have not experienced improvement in their health status. Violence has replaced communicable diseases as the primary cause of juvenile mortality and, currently, over 77% of adolescent deaths are caused by accidents, suicide, and homicide. Increasingly, poverty, life-style, and risk-taking behaviors are influencing the morbidities of youth, with associated sequelae of trauma, adolescent pregnancy, substance abuse, physical/sexual abuse, and most other major health problems of adolescents. Clinicians seem to be interested in addressing the shifting nature of adolescent morbidity, yet are insufficiently trained to be effective. The physician must go beyond traditional clinical medicine and address the social, environmental, and behavioral factors that underlie current morbidity.

The Reproductive Behaviour of the Bell MinerManorina melanophrys

SummaryClarke, M.F. (1988). The reproductive behaviour of the Bell Miner Manorina melanophrys. Emu 88, 88–100.Bell Miners in three study colonies at Bundoora, Victoria, were monogamous. All breeding pairs were assisted in rearing of young by helpers. No extra-pair copulations were observed and it is unlikely that helpers contributed genetically to broods they aided. Breeding occurred in every month of the year and individual breeding pairs made successive attempts within a year. Individuals were capable of breeding nine months after fledging and did not appear to delay breeding to the same degree as many co-operative breeders. Breeding vacancies were filled rapidly. Male breeding vacancies were generally filled by individuals from within the colony whereas female breeding vacancies were filled by individuals from other colonies. Males were occasionally observed to feed their mates before copulation. Mate guarding by both sexes occurred when a new pairbond was being formed and during the period of nest construction. Nests were built by the female breeder. The mean time-interval between commencement of construction and the laying of the first egg was 7.8 ± 1.3 days. The average clutch size was 1.91 ± 0.07 eggs. Incubation was performed by the female over a mean total period of 14.4 ± 0.3 days. The mean number of days between the hatching of the last egg and the fledging of the last nestling was 11.7 ± 0.7 days. Dependent young continued to be fed at a decreasing rate by parents and numerous helpers (up to thirteen) up to an average of 10.6 ± 1.9 weeks after fledging. The mean number of young fledged per attempt was low (0.62 ± 0.22) and highly variable. The major cause of juvenile mortality was predation. Food did not appear to be limiting and there was no evidence of starvation. The large variability in the outcome of a reproductive attempt may have led to the degree of multi-broodedness in Bell Miners and male offspring being philopatric.

Contemporary Threats to Adolescent Health in the United States

Over the past 30 years, adolescents have been the only population in the United States who have not experienced improvement in their health status. Violence has replaced communicable diseases as the primary cause of juvenile mortality and, currently, over 77% of adolescent deaths are caused by accidents, suicide, and homicide. Increasingly, poverty, life-style, and risk-taking behaviors are influencing the morbidities of youth, with associated sequelae of trauma, adolescent pregnancy, substance abuse, physical/sexual abuse, and most other major health problems of adolescents. Clinicians seem to be interested in addressing the shifting nature of adolescent morbidity, yet are insufficiently trained to be effective. The physician must go beyond traditional clinical medicine and address the social, environmental, and behavioral factors that underlie current morbidity.