Helminth community structure of mallards on the southern High Plains of Texas

Date

1993-08

Journal Title

Journal ISSN

Volume Title

Publisher

Texas Tech University

Abstract

This study examined the effects of host age and season on community structure and pattern of helminths in mallards (Anas platyrhynchos) collected on the Southern High Plains (SHP) of Texas during two consecutive winter and summer periods, from 1989-91. From 205 mallards, 24,625 helminth individuals were found, representing 35 species (10 trematode, 13 cestode, 10 nematode, and two acanthocephalan species). Prevalences ranged from <l-70% for individual helminth species across the collective host sample. By taxonomic group, the most prevalent were cestodes (97%) and nematodes (97%), followed by trematodes (87%) and acanthocephalans (4%). Mallards were infected with 8.2 + 0.2 (mean + S.E.) species and averaged 120.1 + 24.0 helminth individuals. The most common microhabitat utilized by helminths was the small intestine, where 18 species occurred, representing at least three feeding guilds. Based on prevalence and abundance values, 16 helminth species were considered common. Acquisition of helminths occurred during summer on the SHP. This region represents the periphery of the mallards breeding range. Most of the helminth species found on the SHP during summer have been reported from the northern breeding grounds, indicating a similar helminth fauna in both regions. Helminth communities had recognizable structure and patterns. Overdispersion was found in the frequency distribution of helminth species and abundance. Individuals of a given species were aggregated in a few host individuals, whereas most host individuals were uninfected or contained few helminth individuals. Host age and season were important factors shaping helminth communities, accounting for heterogeneity in helminth prevalence, abundance, and dominance. Although species richness was similar regardless of host age and season, abundances differed. Of the common helminths, abundances of 10, 13, and 9 species differed by season, host age, and season and age, respectively. By host age, abundances in each of 11 species were higher in juvenile mallards; two species had higher abundances in adults. Seasonal patterns of individual helminth species were less clear, but collectively, helminth abundances were higher in mallards during summer than in winter. Brillouin's index values suggested that helminth infracommunities were diverse. In juvenile hosts, helminth communities typically had large infrapopulations and were species rich, providing the opportunity for communities to be structured by interspecific mechanisms. Adult hosts typically had species-rich communities but infrapopulations were small. Recurrent group analysis indicated that a group of seven helminth species co-occurred across the collective host sample. Recurrent groups formed in mallards during summer were generally larger and more complex than groups during winter. Temporal persistence was demonstrated when five species, Cloacotaenia megalops, Microsomacanthus hopkinsi, Apatemon gracilis, Amidostomum acutum, and Capillaria sp., occurred as recurrent group or associate members in each of the four seasons. Within seasons, recurrent groups found in juvenile hosts were more complex than groups found in adults. Within the various host subpopulations, only a few recurrent group members actually occupied the same microhabitat and were members of the same feeding guild, indicating little if any interspecific competition for resources within mallard hosts among the commonly co-occurring helminth species.

Description

Keywords

Mallard -- Parasites -- Texas, West

Citation