Predicted change in female body volume during pregnancy in two hypothetical lecithotrophic (non-placental) and placentotrophic (placental) live-bearing fish species, assuming an equal female length, offspring number and offspring size at birth (IB = 1): (1) the placental species (dash-dot line) will have a smaller volume during its entire pregnancy than the lecithotrophic species (dashed line) and (2) the relationship for the placental species will show a steeper slope than for the lecithotrophic species, indicating that the difference in body volume will be greatest at the beginning of the pregnancy and gradually diminish towards zero at end of the interbrood interval (redrawn after [9]).

<p>Similar plots could be constructed for frontal or wetted surface area. For heuristic purposes the temporal patterns are assumed linear, because the exact shape of the relationship between female volume and time is currently unknown [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0195976#pone.0195976.ref020" target="_blank">20</a>].