The influence of the environment and infectious disease on amphibian egg laying behavior

This study addresses the importance or infectious disease and the environment on the choice or oviposition site by frogs. The zoospores of some species of oomycetes can colonize and form hyphal colonies that rapidly consume frog eggs. When exposed 10 oomycete zoospores, the eggs of the spring peeper (Pseudcaris crucifer), the bullfrog (Rana catesbeiana), and the southern leopard frog (Rana sphenocephala) all suffered higher mortality than they did under sterile conditions.

In field studies and in controlled laboratory studies, cold water temperatures led to higher rates or infection in R. catesbeiana eggs. This was surprising considering that the hyphae or Saprolegnia grew faster in warmer temperatures when in culture. The frog eggs, however, developed much faster warmer water and were thus able to hatch sooner and escape infection.

The environment affected the timing and location of R. catesbeiana breeding events. Male bullfrogs used low nighttime wind speed, low rainfall, and high daytime temperatures as cues for when to call and attract females. Females relied upon the calling males as their cue for breeding, rather than the weather. The location of male calling sites and breeding sites were aggregated in parts of the pond with more aquatic vegetation.

Infectious disease may also play a role in R. sphenocephala breeding behavior. Eggs were most susceptible to infection in cold temperatures. Adult frogs tended to aggregate their eggs in cold temperatures and aggregation lowered the probability of infection for the eggs.

Spine title: Amphibian egg laying behavior