A survey of freshwater fishes and their macroparasites in the ... - NINA

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NINA Report 635
4.3.2 Effects of host diversity and sample size on the number of parasite taxa
The resampling procedure provides some understanding on how sampling season influences
the diversity of recorded parasite taxa. Figure 4 shows that within one host species, locality
and year (here; the 29 individuals of the most abundant host species Astyanax aeneus from
Rio Sapoa, locality 2, in 1998), we seem to reach a limit at around 5 parasite taxa. Increasing
the number of A. aeneus from Rio Sapoa in 1998 would probably not have yielded more parasite
taxa (green curve). We would probably gain more by increasing the number of host species
in the sample to be dissected from Rio Sapoa in 1998, since the curve for the pooled
sample for all host species (red line; 119 fish, 11 host species) seems not to approach the asymptote.
If all localities in 1998 are pooled, we obtain the black curve (369 fish, 21 species, 8
localities). Some additional parasite taxa seems to be gained by resampling at random from all
localities instead of within Rio Sapoa, but the effect of locality does not seem to be that strong.
Thus, within the season, the number of host species sampled seems to be the most important
factor determining the recorded number of parasite taxa.
No. parasite species
0 5 10 15 20 25 30
0 100 200 300
No. host individuals
1998
Rio Sapoa
Astyanax aeneus
Figure 4 Relation between the number of fish hosts examined and the number of parasite species
identified in the samples from 1998. Green curve: all Astyanax aeneus from Rio Sapoa
(locality 2), red curve: all individuals of all fish species at this locality, and black curve: all fish
from all localities surveyed in 1998. The method is described in section 3.4 on p. 12.
Similarly, we can study how the number of fish of one host species (within locality and year)
affects the number of parasite taxa, how sampling this host species at several localities (in the
same year) affects the number of parasite taxa, and how sampling this host species at several
localities over several years affects the number of parasite taxa. This is illustrated for Astyanax
aeneus in Figure 5. At location 2 (Rio Sapoa) in 1998 we have a sample of 29 individuals of A.
aeneus, but only eight are parasite hosts. When we pool all A. aeneus from all sampled locations
in 1998 together, we find 51 host individuals, but only three more parasite hosts, i.e. a
total of 11 hosts. If we further pool all the three years together, we have dissected 127 individuals
of A. aeneus and found that 31 of them are parasite hosts. Figure 5 shows that the majority
of A. aeneus individuals collected in 1998 were caught on the Rio Sapoa location, and
that the additional individuals from other locations only contributed one more parasite taxon.
The rate of increase in the number of parasite taxa is also reduced when we pool the locations
together, probably due to the high number of fish without parasites. Pooling all three years did