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Energetics of Reproduction in Large‐Littered Cotton Rats (Sigmodon Hispidus)
Author(s) -
Mattingly D. Kevin,
McClure Polley A.
Publication year - 1982
Publication title -
ecology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.144
H-Index - 294
eISSN - 1939-9170
pISSN - 0012-9658
DOI - 10.2307/1937043
Subject(s) - sigmodon hispidus , litter , lactation , reproduction , offspring , ingestion , biology , pregnancy , fecundity , zoology , ecology , endocrinology , medicine , population , genetics , environmental health
Energy costs of reproduction were measured in the laboratory for individual large—littered (° = 7.0) cotton rats, Sigmodon hispidus, from Kansas, and less extensively for individual small—littered (° = 4.7) cotton rats from Texas. These estimates were compared with previously studied small—littered (° — 5.0) S. hispidus from Tennessee. Reproductive Kansas S. hispidus (KSh) increased ingestion above nonreproductive rates by 19% during pregnancy and 111% during lactation. This represents extra ingestion of 766 kJ during 26 d of pregnancy and 2111 kJ during 12 d of lactation. Extra ingestion throughout reproduction was dependent on litter size. Total extra ingestion cost per 12—d—old KSh offspring was 415 kJ, a constant unaffected by litter size. Digetive efficiency of KSh rats fed a commercial standard lab chow was 85% and did not changes as a result of pregnancy and lactation. Metabolic rate of reproductive KSh rats was not significantly different from that of nonreproductive rats. The average body mass of KSh females on the day of conception was 175 g, vs. 169 g at the end of 12 d of lactation, a loss of 6 g. This loss of body mass during reproduction increased with increasing litter size: KSh females giving birth to litters of eight to ten young lost an average of 19 g below conception mass, while females giving birth to five to seven young gained an average of 1 g. KSh young averaged 6.8 g at birth and 21.7 g at 12 d of age. Reproductive Texas S. hispidus (HSh) increased ingestion over nonreproductive rates by 22% during pregnancy and 70% during lactation. This represents extra ingestion of 854 kJ during pregnancy and 1161 kJ during lactation. Total extra ingestion cost per 12—d—old offspring was 434 kJ for HSh litters. The average body mass of females on the day of conception was 134 g and, at the end of 12 d of lactation, averaged 138 g. HSh young averaged 6.7 g at birth and 1802 g at 12 d of age. Kansas cotton rats produced relatively large litters and large individual young primarily by markedly increasing ingestion and drawing upon maternal storage during lactation. Both of these responses were probably facilitated by the KSh female's large body size. These results and comparisons among similarly studied species suggest the importance of the common constraits and correlated responses associated with changes in body size and litter size when considering energy utilization during reproduction.