Parental male and female convict cichlids assess and respond to threats differently depending on intruder species.

In this field experiment, we presented pairs of monogamous convict cichlids with different intruders (conspecific and either cichlid or non-cichlid heterospecific) and observed the aggressive behavior of the pair to determine if pairs adjust aggression based upon species of intruder. We predicted that pairs would be more aggressive to conspecifics as these intruders represent multiple threats. The overall pair aggression was significantly higher to the conspecific intruder than to either heterospecific intruder. We also predicted that within pairs, the sexes might differ in how they assessed the risk represented by the intruders and might respond differently. Indeed, females were significantly more aggressive to the conspecific than to either heterospecific whereas males were more aggressive to the conspecific only compared to the non-cichlid heterospecific. These results suggest parental convict cichlids differently assess the risk posed by an intruder and then adjust aggression to different species of intruder. It also supports that the aggressive roles within a pair are flexible and that males and females modulate their behavior differently in response to different species of intruders perhaps based on differences in risk assessment.

Accumulation of nonessential trace elements (Ag, As, Cd, Cr, Hg and Pb) in Atlantic horseshoe crab (Limulus polyphemus) early life stages.

During early development, benthic organisms can accumulate nonessential trace elements through aqueous and particulate sources. This study investigated the accumulation of Ag, As, Cd, Cr, Hg and Pb in Atlantic horseshoe crab (Limulus polyphemus) pre-spawned eggs, embryos, and developing larvae collected from 5 sites on Long Island, NY and compared these concentrations to that found in sediment, pore water, and overlying water. All investigated elements were detected in embryos and larvae at all sites. Arsenic was found at the highest concentration in each life stage across all 5 sites, followed by Ag, whereas Cd, Hg and Pb concentrations varied between sites. Chromium was not detected in pre-spawned eggs, but was present in embryos and larvae at all sites, however, along with Hg, significantly increased from embryo to larvae at most sites. We conclude that observed accumulation patterns are likely a result of abiotic factors, differences in uptake pathways between life stages and the rate of excretion. Future laboratory studies are required to understand the factors influencing the aqueous and dietary uptake of nonessential trace elements in the early life stages of Atlantic horseshoe crabs.

Maternal transfer of trace elements in the Atlantic horseshoe crab (Limulus polyphemus).

The maternal transfer of trace elements is a process by which offspring may accumulate trace elements from their maternal parent. Although maternal transfer has been assessed in many vertebrates, there is little understanding of this process in invertebrate species. This study investigated the maternal transfer of 13 trace elements (Ag, As, Cd, Co, Cr, Cu, Fe, Hg, Mn, Ni, Pb, Se, and Zn) in Atlantic horseshoe crab (Limulus polyphemus) eggs and compared concentrations to those in adult leg and gill tissue. For the majority of individuals, all trace elements were transferred, with the exception of Cr, from the female to the eggs. The greatest concentrations on average transferred to egg tissue were Zn (140 µg/g), Cu (47.8 µg/g), and Fe (38.6 µg/g) for essential elements and As (10.9 µg/g) and Ag (1.23 µg/g) for nonessential elements. For elements that were maternally transferred, correlation analyses were run to assess if the concentration in the eggs were similar to that of adult tissue that is completely internalized (leg) or a boundary to the external environment (gill). Positive correlations between egg and leg tissue were found for As, Hg, Se, Mn, Pb, and Ni. Mercury, Mn, Ni, and Se were the only elements correlated between egg and gill tissue. Although, many trace elements were in low concentration in the eggs, we speculate that the higher transfer of essential elements is related to their potential benefit during early development versus nonessential trace elements, which are known to be toxic. We conclude that maternal transfer as a source of trace elements to horseshoe crabs should not be overlooked and warrants further investigation.

Environmental exposure of Atlantic horseshoe crab (Limulus polyphemus) early life stages to essential trace elements.

This study investigated the accumulation Co, Cu, Fe, Mn, Ni, Se, and Zn in Atlantic horseshoe crab (Limulus polyphemus) early life stages (egg, embryo and larvae) and compared the concentrations to the concentration of each element in sediment, pore water and overlying water for 5 sites across Long Island, NY. For the majority of the sites, all essential trace elements accumulated in the embryos and larvae. However, many of the embryos and larvae at specific sites presented different concentration patterns which had no apparent relationship with the local habitat sediment and water values. Generally, Cu, Fe, and Se sequentially increased from egg stage through larval stages for the majority of sites, while Co, Mn, and Ni only did for a few sites. Zinc also showed an increase across sites from embryo to larval stage, however was the only one to show a decrease in concentration from egg to embryo stage at all sites. Interestingly, Mn at Manhasset Bay presented embryo and larval stages to be 50 fold greater than all other sites while the egg stage showed similar values to other sites; this high degree of uptake could be due to a high concentration in the overlying water. All essential trace elements can be accumulated from the environment but greater concentrations may be influenced by abiotic factors and the predominant uptake route (aqueous versus diet) at each life stage. Future laboratory experiments are required to investigate factors that influence essential trace element accumulation and loss in horseshoe crab early life stages.