Allocation patterns in modes of reproduction in two facultatively sexual cryptic rotifer species

Abstract

Many zooplankters rely on diapausing stages to survive unsuitable conditions in time-varying habitats. In facultativesexualrotifers, reproductive effortallocatedtothe sexuallyproduced diapausingeggs isat the expenseofthe subitaneousparthenogenetic eggs, generatingatrade-offbetweencurrentand future population growth.Thetimingand the amountof sex (the sexual pattern) affect diapausing-egg production. This switch to sex is complex because the reproductivemode is separated in distinct females: asexual (female-producing), unfertilized sexual (male-producing) and fertilizedsexual (diapause-egg-producing). We studied sexual patterns and life-history variation of these females in two crypticspecies (Brachionus plicatilis and Brachionus manjavacas) co-occurring in Spanish ponds. Results revealed species-specific dif-ferencesinsexual pattern;B. plicatilis had an earlierand higher sex allocation. Female types allocated resources different-ly among life-history traits, revealing relationships between lifespan and reproductive traits that demonstrate the cost ofreproduction. Sexual females reproductive traits showed between-species differences. Brachionus manjavacas unfertilizedfemales produced more sons earlier and at a greater daily rate than B. plicatilis ones. Moreover, B. manjavacas fertilizedfemales had higher relative allocation per diapausing egg than those of B. plicatilis. We relate these differences to the en-vironmentaluncertaintyfacedbyeachspecies,anddiscusstheirimplicationsforcompetitiveoutcome.KEYWORDS: density threshold for sex initiation; life-table parameters; female reproductive types; competition;diapausing eggs