Characterization of unilateral conjunctival inoculation with Mycoplasma gallisepticum in house finches.

House finches in much of the continental United States experience annual epidemics of mycoplasmal conjunctivitis, caused by the bacterial pathogen Mycoplasma gallisepticum (MG). Although evidence suggests that natural infections typically begin unilaterally, experimental inoculations of songbirds with MG to date have all been administered bilaterally. Furthermore, studies of free-living finches find more severe clinical signs of mycoplasmal conjunctivitis in left versus right eyes, but the mechanisms underlying this side bias remain unknown. Here, we characterized unilateral inoculation of house finches with MG, and tested whether differential susceptibility of left versus right conjunctiva explains the side bias in disease severity of free-living finches. We directly inoculated house finches in either the left or right conjunctiva and characterized resulting disease severity and pathogen load throughout the course of infection. As expected, unilateral inoculation resulted in significantly more severe conjunctivitis, as well as higher conjunctival bacterial loads, on whichever side (left or right) birds were directly inoculated. However, in 55% of cases, unilateral inoculations resulted in bilateral disease, and in 85% cases there was evidence of bilateral infection. The overall severity of disease did not differ for birds inoculated in the left versus right conjunctiva, suggesting that physiological differences between the conjunctivae cannot explain the side bias in disease severity of free-living birds. Instead, laterality in exposure, perhaps due to feeding handedness, likely explains the detected field patterns. RESEARCH HIGHLIGHTS House finches show more severe disease in the directly inoculated conjunctiva. Unilateral inoculations lead to high rates of bilateral infection and disease. Overall disease severity does not differ for the left- or right-inoculated conjunctiva. Laterality in exposure likely explains the left-side bias in natural infections.

Incidental spatial memory in the domestic dog (Canis familiaris).

We built upon previous work by Fujita et al. (2012, Animal Cognition, 15(6), 1055-1063) to create an experiment that investigated the presence of incidental memory for the spatial location of uneaten food in the domestic dog. Here, we dissociated potentially incidental spatial memory from the incidental memory for the characteristics of objects, in this case, food bowls. Eighteen household domestic dogs of various breeds and age were presented with four bowls. Each bowl contained either a novel object, treats the dog could consume, treats it could not consume, or it was left empty. Following a delay, the dogs returned to the laboratory and were presented with empty bowls in the same spatial orientation as the initial exposure and could move freely between bowls. This experiment required no previous training outside of basic obedience and so avoids the possibility that performance on the test was a conditioned response. We hypothesized that domestic dogs would be able to remember the location of uneaten food when presented with an unexpected memory test. We found that dogs in this study showed no evidence that they encoded spatial location in the absence of other cues that could be used to distinguish food bowls at specific locations. This suggests that dogs in previous experiments were more dependent on incidentally encoding the "what" and "in what" of this task than the "where," in the absence of features making each location distinct.