19 September, 2013

Mother scorpions are less effective predators

Webber and Rodriguez-Robles has recently published a study investigating if potential reproductive tradeoffs limit the predatory efficiency of female Centruroides sculpturatus Ewing, 1928 (Buthidae).

Females with scorplings on their back were less effective hunters than non-gravid females. Interestingly, gravid females hunted prey as efficient as non-gravid females. Overall it seems that reproduction represent a cost in females by reducing their predatory efficiency during the brooding period.

Life history tradeoffs may result from temporal and physiological constraints intrinsic to an  organism. When faced with limited time and energy, compromises occur and these resources  are allocated among essential activities, such as body growth, maintenance, foraging, mating,  and offspring care. We investigated potential tradeoffs that may  occur between reproductive  activities  and  feeding  performance  in  female  Arizona  Bark  Scorpions  (Centruroides  sculpturatus)  by  comparing  the  time  taken  to  capture  prey  between  non-reproductive  and  reproductive  females  (gravid  females  and  females  exhibiting  maternal  care,  i.e.  carrying  offspring on their backs).
Gravid  females  were  as  efficient  at  catching  prey  as  non-gravid  females.  To  control  for  variation in the duration of the maternal care period, we removed all  offspring from all postparturient females after 5 days. Brooding females and females  24 hours following offspring  removal (FOR) did not successfully capture prey within the 900-second trial period. Twentyeight  days  FOR,  females  caught  prey  faster  than  females  displaying  maternal  care  and  females 24 hours FOR, but were not as efficient at catching prey  as non-gravid and gravid  females.  When  pursuing  prey,  C.  sculpturatus exhibiting  maternal  care  used  an  active  foraging  strategy  more  frequently  than  non-gravid,  gravid,  and  females  28  days  FOR.  In  contrast, non-gravid, gravid, and females 28 days FOR used active and ambush foraging with  similar frequency.
Our data suggest that reproduction does not significantly reduce the predatory efficiency of  gravid  C. sculpturatus, and that these females can cope with increasing body mass and  the  physiological costs of gestation. However, the observation that brooding females and females  24  hours  FOR  did  not  catch  prey  within  the  trial  period  indicates  that  maternal  care  significantly reduces predatory efficiency in these scorpions. Females 28 days FOR were still  not  as  efficient  at  catching  prey  as  non-gravid  and  gravid  females,  suggesting  that  reproductive  costs  extend  for  at  least  4  weeks  after  the  end  of  the maternal  care  period.  Preferential  use  of  an  active  foraging  strategy  by  brooding  females  may  increase  prey  encounter  rates,  allowing  the  scorpions  to  more  rapidly  replenish  energy  reserves  depleted  during  reproduction.  However,  active  foraging  may  be  energetically costly  and  increase  predation risk for brooding females. Our findings regarding antagonistic interactions between  reproduction  and  feeding  in  female  C.  sculpturatus demonstrate  the  pervasive  nature  of  reproductive costs for viviparous females, and may provide insight on factors that influence  the diversity of reproductive strategies observed in nature. 

Webber MM, Rodriguez-Robles JA. Reproductive tradeoff limits the predatory efficiency of female Arizona Bark Scorpions (Centruroides sculpturatus). BMC Evol Biol. 2013 Sep 14;13(1):197. [Free full text]

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