File:American malacological bulletin (1987) (17535929173).jpg

Title: American malacological bulletin
Identifier: americanmal4519861987amer (find matches)
Year: 1983 (1980s)
Authors: American Malacological Union
Subjects: Mollusks; Mollusks
Publisher: (Hattiesburg, Miss. ?) : (American Malacological Union)
Contributing Library: Smithsonian Libraries
Digitizing Sponsor: Biodiversity Heritage Library

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McMAHON AND WHITEHEAD: SHELL VARIATION IN ANCYLUS 115 .40- I.35-
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I.30- I .25- I.20 - 0.2 0.3 0.4 0.5 mm AL / 30 DAYS 0.6 Fig. 6. Allometry of estimated population mean shell length:aperture width ratios (AL/AW) with mean annual population growth rate in Irish Ancylus fluviatilis populations. The y axis is the mean shell AL/AW ratio estimated for a 4.5 mm AL standard individual from least squares linear regression equations relating AL/AW to AL for each population collected. The x axis is annual population growth rate in mm AL per 30 days. The open circles are the estimated AL/AW ratio for each population for which collection sites are indicated by the adjacent numbers (see Tables 1 and 2). The vertical bars are standard errors of the means. The solid line represents the best fit of a significant (P < 0.001) log-log least squares linear regression equation relating estimated AL/AW to annual population growth rate (see Table 4 for regression parameters). ference in mean AL/AW ratio of the 1982 and 1984 adult generations was observed only in the Gannew Brook popula- tion, Co. Donegal (sites 7 and 27R, Table 6). In this popula- tion the mean AL/AW ratio was significantly greater in 1982 (mean AL/AW = 1.328) than in 1984 (mean AL/AW = 1.287) (Table 6). The mean AL/SH and AW/SH ratios of individuals from this population were also significantly greater in 1984 (1982: mean AL/SH = 2.098; AW/SH = 1.583, 1984: mean AL/SH = 2.199, AW/SH = 1.709), indicating that they had less elevated shells with rounder apertures than those taken in 1982 (Table 6). Similar significant increases in the mean AL/SH and AW/SH ratios of adult limpets were also record- ed for two other populations in 1984. The mean AL/SH and AW/SH ratios of adult individuals from an unnamed stream in Fintragh, Killybegs, Co. Donegal, were 2.208 and 1.673, respectively, in 1984 (collection 29R), while these values were 2.150 and 1.626 for adults taken in 1982 (collection 9). Similar- ly, the mean AL/SH and AW/SH ratios of adults taken in 1984 at Croleavy Lough Outlet, Upstream, Co. Donegal (collection 31R) were 2.252 and 1.726, respectively, while those of adults taken there in 1982 (collection 11) were significantly lower at 2.184 and 1.660 (Table 6). None of the significant dif- ferences in mean AL/AW, AL/SH and AW/SH ratios observed in populations collected both in 1982 and 1984 could be at- tributed to allometries associated with changes in mean SL or growth rate between years of collection, as these parameters for the 1981A and 1983A generations at each of these three sites were essentially the same prior to the 1982 and 1984 collections (Tables 1, 2). DISCUSSION Russell-Hunter ef al. (1981) suggest that freshwater molluscs can display four different relationships between shell CaC03 content and habitat water calcium concentration.

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