Co-Exposure with the Herbicide 2,4-D Does Not Exacerbate Batrachochytrium salamandrivorans Infection in the Italian Crested Newt (Triturus carnifex)

Abstract

Amphibians face a multitude of threats and therefore make a prime example of the current biodiversity crisis. Multiple amphibian stressors in anthropogenic landscapes include infectious diseases and agrochemicals. Synergic effects between these stressors may increase the negative impact of infections on amphibian health. In a 56-day trial, we assessed the impact of co-exposure to the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) and the pathogenic fungus Batrachochytrium salamandrivorans (Bsal) on infection parameters (infection intensity and disease severity) and health (body condition and telomere length) in Italian crested newts (Triturus carnifex). Twenty days post-inoculation with Bsal, newts were either exposed to 2,4-D for 12 days or not exposed (control). Most newts developed high infection loads that steadily increased towards the end of the trial. While body condition was negatively correlated with pathogen burden, only one out of 23 animals died. Telomere length remained unaffected by the pesticide and the pathogen. The 2,4-D treatment did not exacerbate Bsal infection. Most newts survived almost two months with significant pathogen loads; thus, even in a pesticide-infested environment, T. carnifex could be an important long-term Bsal reservoir for co-occurring species on the Italian peninsula, a urodele diversity hotspot.

Keywords: agrochemicals; amphibian conservation; chytridiomycosis; emerging infectious diseases; newts; pollution.

Figure 1

Individual Bsal loads curves separated by treatment (2,4-D + Bsal, blue vs. Bsal, orange) and highlighting the individual that died (TC9, in black on the right panel) (A). Average Bsal load per treatment over time (2,4-D + Bsal treatment in black, and Bsal treatment in light gray) (B). The shaded area around each line represents the 95% confidence interval (CI) for the mean Bsal load at each time point. Bsal load is log10-transformed (log-tr).

Figure 2

Total Bsal load per 2,4-D treatment group (2,4-D + Bsal vs. Bsal). Each dot represents an individual. The black line is the median, the box shows the interquartile range (IQR), and the whiskers indicate the range of the data excluding outliers. Total Bsal load was measured as the area under the curve of Bsal load drawn from weekly qPCRs. Three individuals in the 2,4-D + Bsal treatment and one individual in the Bsal treatment did not become infected with Bsal and are thus not represented here. Bsal load is log10-transformed (log-tr).

Figure 3

Correlation between body condition at the end of the experiment (Day 56) and total Bsal load among Bsal-exposed individuals. Each dot represents an individual. The black line shows the linear regression, and the shaded area is the 95% confidence interval. Total Bsal load was measured as the area under the curve of Bsal load drawn from weekly qPCRs. Bsal load is log10-transformed (log-tr).