An Overview of Dioxin-Like Compounds, PCB, and Pesticide Exposures Associated with Sexual Differentiation of Neuroendocrine Systems, Fluctuating Asymmetry, and Behavioral Effects in Birds

Abstract

Dioxin, polychlorinated biphenyls (PCBs), and pesticides impact neural systems in birds due to interference with sexual differentiation. Early endocrine disrupting chemical (EDC) effects may delay maturation and have long-term effects on lifetime reproduction, especially in precocial birds that complete sexual differentiation prior to hatch. Semi-altricial and altricial species appear more resilient to EDC effects and show a gradient in sensitivity, especially in the neuroplastic song system. Embryonic steroid exposure occurs via maternally deposited steroids followed by embryo produced hormones; EDCs potentially affect these developing systems. As such, EDCs can impact lifelong fitness by acting on neural systems that regulate reproduction, metabolism, and behavior.

Expression Profiles of Reproduction- and Thyroid Hormone-Related Transcripts in the Brains of Chemically-Induced Intersex Frogs

“…EDCs can detrimentally affect neuroendocrine control mechanisms and sexual behavior in vertebrates [Martiniuk et al, 2006;Mennigen et al, 2008;Ottinger et al, 2009;Hayes et al, 2010]. Therefore, one objective of this study was to identify genes in the brain that are susceptible to change if sex steroid levels are chemically altered in developing frogs.…”

Uptake of radiolabeled 3,3′,4,4′‐tetrachlorobiphenyl into Japanese quail egg compartments and embryo following air cell and albumen injection

“…Furthermore, a number of egg injection studies have effectively established the impacts of hydrophilic and hydrophobic vehicles and compounds, including PCBs, dioxins, PBDEs, dibenzofurans, perfluorooctane sulfonate, and methyl mercury [45,51,52,[54][55][56][57][58][69][70][71][72][73][74][75]. These studies have contributed to our understanding of toxicity profiles and measurement endpoints, and have given us data useful in directly estimating the egg concentrations in wild birds and the modes/timing of maternal transfer [10,63]. Treatment prior to incubation allows the compound to partition into the matrices of the egg components, further mimicking maternal deposition.…”

“…The percentage of 14 C PCB 77 present/total injected in shell samples varied according to embryonic day and vehicle (Table 1). Table 2 shows the MANOVA for 14 C PCB 77 uptake in a matrix of comparison of the different groups over embryonic day (1,5,10), vehicles (fatty acid and corn oil), and injection sites (air cell and albumen). Significant changes (p < 0.0001) in 14 C PCB 77 concentration confirmed movement of PCB 77 between the egg components over embryonic development, with no difference associated with vehicle type or injection site.…”

Evolutionary Perspectives on Sex Steroids in the Vertebrates

“…In cases of endocrine disruption, exposure levels are typically too low to have toxic or acute effects on adults (Colborn et al 1993), but affect organisms during critical organizational periods of early life stages (Guillette et al 1995). Tissue contaminant levels previously considered safe are sufficient to alter endogenous chemical mediation in fish Jobling et al 2006), amphibians (Hayes et al 2002;Hayes et al 2006;Hayes et al 2010), reptiles (Crews et al 1995;Guillette et al 2000), birds (Ottinger et al 2009), and mammals (Colborn et al 1993). …”