Influence of contaminant transfer from mom to pup?

This project aims to understand how contaminant transfer from mother to pup may change over the course of gestation using the Bonnethead as a model for placental elasmobranch species.

In other vertebrates, exposure to contaminants early in development has negative implications for health outcomes. Because development is dynamic, embryos may be at greater risk of exposure at certain periods of gestation than others. However, before we can begin to quantify what these effects may be, we need to understand what point in utero represents the most contaminant exposure risk to offspring due to maternal offloading. Potential negative effects from contaminant exposure are often not considered when evaluating human impacts on species. However, the manifestation of sublethal effects from exposure in early development may have implications for animal survival and fitness after birth.

Maternal offloading is the process whereby females unknowingly pass contaminants to their offspring during reproduction, and has been documented to occur across vertebrate species, including elasmobranchs, regardless of whether they lay eggs or give birth. In placental elasmobranchs, where females tend to invest substantial resources into the creation of precocious young, maternal offloading may occur in two phases: initially at ovulation through the creation of a relatively large egg and potentially continuously after a placental connection is formed between the embryo and its mother. Maternal transfer potential could differ between these two routes based on physiological differences between the structures. For example, yolky ovulated eggs could be a better conduit for contaminant transfer because many contaminants are lipid-loving, and eggs tend to be high in fat. By contrast, contaminant transfer through the placenta could be more difficult and potentially limit the amount and type of contaminants that can be passed to embryos via this route. This could lead to a situation where embryos may be exposed to different concentrations of contaminants at different points in development. Therefore, depending on which developmental periods are the most sensitive to contaminant exposure (i.e. early versus middle versus late), this could influence how effects will manifest in embryos.

In addition, historic estimations of females’ ability to lower their own contaminant body burden by offloading to offspring often assume that no additional contaminant input is occurring during pregnancy. In other words, the contaminants that pregnant females may be acquiring through food are assumed to be negligible. As pregnancy is a highly demanding, energetic process, it seems unlikely that females are fasting during their entire gestational cycle. Therefore, this previous assumption oversimplifies the reproductive process, resulting in a conservative view of females’ ability to maternally offload contaminants, which may also underestimate the degree of embryo exposure during this sensitive time in development. This study aims to close this gap in knowledge using a model placental species (Bonnethead) to understand how maternal offloading ability may change throughout gestation when contaminant input through feeding occurs.

•  Objective 1: A suite of organochlorine contaminants will be analysed in maternal liver and embryonic tissues across various stages of pregnancy. Females will be opportunistically sampled from four distinct categories in their reproductive cycle that represents important inflection points in nutritional provisioning by mothers to embryos: pre-ovulation/ovulating (yolk “baseline” values before embryo development), early-term pregnancy (embryo dependent on yolk only), mid-term pregnancy (placental connection formed but embryos are underdeveloped), and late-term pregnancy (embryos are well developed and near birth size).
• Objective 2: After contaminant quantification, the degree of maternal offloading will be calculated for the total sum of contaminants and by group (i.e. PCBs, DDTs, non-DDT pesticides), and potentially for individual contaminants depending on detection rates. Rates of maternal offloading for each contaminant group will then be compared across reproductive stages.
• Objective 3: Contaminant signatures will be compared in maternal-embryo pairs of tissues across pregnancy. Multivariate analyses will be used to determine if contaminant signatures between mothers and embryos at each gestational stage look similar throughout gestation or deviate after placental establishment (i.e. mid to late pregnancy). A different signature later in gestation could be indicative of contaminants sourced from prey ingested during pregnancy that are transferred directly to embryos and not incorporated into maternal tissues.

Public presentation at MODS: Save Our Seas Distinguished Speaker Series : Sharks and Pollution