Shift from income breeding to capital breeding with latitude in the invasive Asian shore crab Hemigrapsus sanguineus

Abstract

Organisms vary in the timing of energy acquisition and use for reproduction. Thus, breeding strategies exist on a continuum, from capital breeding to income breeding. Capital breeders acquire and store energy for breeding before the start of the reproductive season, while income breeders finance reproduction using energy acquired during the reproductive season. Latitude and its associated environmental drivers are expected to heavily influence breeding strategy, potentially leading to latitudinal variation in breeding strategies within a single species. We examined the breeding strategy of the Asian shore crab Hemigrapsus sanguineus at five sites spanning nearly 10° of latitude across its invaded United States range. We hypothesized that the primary breeding strategy of this species would shift from income breeding to capital breeding as latitude increases. We found that though this species' breeding strategy is dominated by capital breeding throughout much of the range, income breeding increases in importance at lower latitudes. This latitudinal pattern is likely heavily influenced by the duration of the foraging and breeding seasons, which also vary with latitude. We also found that reproductive characteristics at the northern and southern edges of the invaded range were consistent with continued range expansion. We suggest that the reproductive flexibility of the Asian shore crab is a key facilitator of its continued invasion success. Our results highlight the influence of latitude on the breeding strategy of a species and emphasize the need for further research regarding the ecological importance and implications of flexibility in breeding strategies within species.

Figure 1

Residual ovary mass of Hemigrapsus sanguineus across months for each of the five sampling sites, indicated by the state abbreviation in the upper right corner of each plot. Heavy black line shows median value, boxes encompass the interquartile range (i.e., 25th–75th percent of the data), whiskers encompass 1.5 × the interquartile range, and circles represent data points that fall outside that range. Letters over the boxplots show statistical significance within each site only (from site-specific ANOVAs and Tukey’s tests), where boxplots with the same letter are not significantly different.

Figure 2

Residual ovary mass of Hemigrapsus sanguineus at the Connecticut sampling site where sampling occurred more frequently. The data show three primary reproductive peaks representing three distinct clutches occurring up to Julian sampling date 93 and around sampling dates 165 and 226. The boxplots corresponding to these primary reproductive peaks are colored gray. Boxplots are as described in the caption for Fig. 1.

Figure 3

Residual egg mass of Hemigrapsus sanguineus across months for each of the five sampling sites, indicated by the state abbreviation in the upper right corner of each plot. Boxplots and letters over the boxplots are as described in the caption for Fig. 1.

Figure 4

Comparison of pre-reproduction energy storage (energy contained in the hepatopancreas and ovary, as measured by mass; white bars) to egg mass of first clutch (gray bars) in Hemigrapsus sanguineus indicates which breeding strategy is dominant at a site, where storage mass > egg mass is consistent with capital breeding, and storage mass < egg mass indicates income breeding. Error bars show one standard error from the mean. Gray boxes above each pair of bars indicate the predominant breeding strategy at that site. Sampling locations are listed along a decreasing latitudinal gradient from left to right.