Effects of vinclozolin, an anti-androgen, on affiliative behavior in the Dark-eyed Junco, Junco hyemalis.

Endocrine disrupting chemicals (EDCs) produce changes in physiology and behavior via diverse mechanisms including acting as hormone mimics or antagonists, affecting intracellular signaling pathways, and altering hormone production pathways. The fungicide vinclozolin acts as an anti-androgen and is known to affect affiliative behaviors in rodents, fish and amphibians. To investigate the possible effects of exposure to EDCs on reproductive behavior in a wild population of songbirds, we examined the effects of vinclozolin in wild-caught Dark-eyed Juncos (Junco hyemalis). For this and many other temperate songbird species, testosterone has powerful activational effects on affiliative behaviors in adulthood. We hypothesized that vinclozolin would affect male behaviors associated with female preference. Male juncos received daily oral gavage for 10 weeks with 2mM vinclozolin in vehicle or vehicle alone. Juncos were photostimulated (16L:8D) to induce breeding behavior. Each pair of a treated and non-treated male was presented to an estrogen-primed female to assess female preference. Seven of eight females exhibited a strong preference for a male exposed to vinclozolin over a control male (p=0.01). The only significant difference in measured male behaviors was increased beak wiping in controls (p=0.006) and there was no difference in gonad size or brain weight (p>0.05 for each). Our data suggest that estrogen-primed female juncos prefer to associate with male juncos exposed to this anti-androgen. This finding demonstrates that environmentally occurring anti-androgens can affect the social behavior of this species. To our knowledge, this is the first study to show that vinclozolin has effects on the social behavior of songbirds.

Androgen receptor location in the dark-eyed junco using a probe for in situ hybridization histochemistry generated from zebra finch cDNA.

Due to the role of sex steroids, namely testosterone (T), in the development and production of song in songbirds, androgen receptor (AR) densities in the brain regions controlling this behavior (i.e., the song control system) have long been studied. Many methods have been used to determine AR density and location to investigate the functional role of T in song development and production; however, a riboprobe developed from zebra finch (Taeniopygia guttata) cDNA was shown to be much more sensitive than previous methods. The zebra finch is a common model for song development and is sexually dimorphic, but does not breed seasonally or display seasonal changes in song control region volume. In this study, we used this riboprobe for in situ hybridization histochemistry (ISHH) to describe AR mRNA location in the brain of the dark-eyed junco (Junco hyemalis), a seasonally breeding model for which T has been shown to be important. Additionally, we provide a detailed comparison of AR mRNA location between these species. We found that this probe is indeed highly sensitive. We detected AR mRNA in four major regions of the song control system (HVC, MAN, RA and Area X). Additionally, we found that the location of AR mRNA in other regions varied only slightly between these two species. These findings suggest that this method is suitable for use across songbirds and it could be useful in the ongoing attempts to elucidate the roles of sex steroid hormones on the development of this and other sex steroid dependent behaviors in songbirds.

Dietary phytoestrogens and photoperiodic response in a male songbird, the Dark-eyed Junco (Junco hyemalis).

Many commercial bird diets are made with soy products that contain phytoestrogens (i.e., plant compounds that have weak agonist activity at estrogen receptors), but the effects of these compounds on bird physiology and behavior are largely unknown. The primary phytoestrogens present in soy are the isoflavones genistin and diadzin, which have been shown to affect reproductive measures in many taxa. Two groups of wild-caught male Dark-eyed Juncos (Junco hyemalis) were fed a diet either made with water-washed soy protein (soy(+)) or made with soy protein that had been alcohol-washed to extract isoflavones (soy(-)). Both groups exhibited a photoperiodic response to long days. Plasma luteinizing hormone (LH) concentrations increased within the first week of long day (LD) exposure for both groups, and over the course of the experiment LH was higher in the soy(+) group, although concentrations for both groups were lower than have been reported in free-living juncos. The rate of cloacal protuberance (CP) growth was significantly affected by diet, with the soy(-) birds beginning to increase their CPs about a week faster than soy(+) birds after exposure to LD. There was no group difference in food intake, fat score, body mass, or behavioral measures during the study or in testis weight at the end of the study. Although effects of dietary phytoestrogens detected were subtle (i.e., rate of CP growth), those investigating subtle effects of hormonally active substances (e.g., endocrine disruptors) or environmental cues affecting the reproductive axis in songbirds may want to consider eliminating phytoestrogens from their experimental diets.