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The general female bias in body size of animals is usually attributed to fecundity selection. While many studies have demonstrated a positive relationship between body size and fecundity, the most common interpretation of fecundity selection is that larger females have larger abdomens and can hold more eggs, yet the relationship between abdomen size and fecundity has rarely been examined. For the waterstrider, Aquarius remigis, we find a significant relationship between body size and fecundity and demonstrate that the target of fecundity selection is abdomen size. Thus, larger females have higher fecundities because they have larger abdomens and not because of their total size per se. The rate at which fecundity increases with increasing abdomen size exceeds that which would be expected due to a simple volume constraint and suggests that other factors, such as increased ability to obtain resources, may contribute to the increase in fecundity with body size. Selection intensities estimated from our data indicate that fecundity selection could be a significant selective force on both total and abdomen lengths. Previous studies have found that abdomen size increased faster than body size and thus, larger females had relatively larger abdomens. The relationship of abdomen length and thorax length in A. remigis is hypoallometric and indicates that larger females have relatively smaller abdomens. We hypothesize that this may reflect conservation of abdomen size in females developing under poor conditions. Finally, while egg size is not directly related to body size, we find a trade-off between egg size and number when female abdomen length is held constant, suggesting that selection on egg size may influence abdomen length only indirectly through its effects on fecundity.

\Ve examined morphological variation among populations of' the stream-dwelling waterstrider, Aquarius rem@. A previous analysis of allnzyme variation along a transect from southern Quchcr to southern North Carolina revealed two distinct 'types' of A . rm&, north and south of a transition zone in southern New York and northern Prnnsylvania. T o assess the conrordanre of morphological and allozyme differentiation, adults were sampled liom 15 populations along thr original transect, as well as I 1 additional populations in New York, Connecticut and New Jersey. Eight measurements of leg and body sizr "ere taken of presewed individuals. Univariate and multivariate analyses (multiple regression, PCA, discriminant analysis) reveal significant difyerentiation between northern and southern populations with a transition zone between latitudes 39" and 42" north. Strong clines within each region and a clear transition between regions support prrvious suggestions that there are two distinct 'types' of' this species in eastern North Amerira. Tiir transition zone in morphology coincides with that rrvealed by the allozynic vaiiation, but extends further south. The covariance of allozyme frequency and morphometric traits suggests that differentiation has occurred through cicariance and secondary contact, and that in this system, cladistic and adaptive differentiation are coupled. ADDITIONAI, KEY WORDS: body size ~ morphology -PCA ~ discriminant analysis transition zone ~ vicariance ~ speciation.

Hebrew translations of the Kaufman Assessment Battery for Children (KABC) and the Vineland Adaptive Behaviour Scales (VABS) were administered to 17 Israeli males with fragile X and 17 with Down syndrome matched for chronological and mental ages. When differences in the initial baselines were considered, the pattern of findings was generally consistent with previous reports. On the K-ABC, the males with fragile X scored higher on some subtests of the Simultaneous Domain but not on any of those of the Sequential Domain. On the VABS, superior scores of the males with fragile X on the Daily Living Skills and Communication domains is consistent with prior evidence of their relative strength on the former and the specific weakness of persons with Down syndrome on the latter. These differences between the males with fragile X and Down syndrome with regard to functioning on various domains and subdomains highlight the need to carefully examine the profiles of aetiologically homogeneous groups of persons.