Cooperative breeding in reindeer (Rangifer tarandus): testing the hypothesized causes of allosuckling and allonursing.

Cooperative breeding is a social system in which members of the social group provide parental care to the offspring of other parents. The suckling by offspring from females other than their mother is referred to as allosuckling. The provision of milk to the offspring of other mothers is referred to as allonursing. Allonursing is often believed to have evolved by kin-selection, however, other causes have been hypothesized. My thesis examines the misdirected parental care, kin-selection, reciprocity, milk evacuation, improved nutrition, compensation hypotheses, and these hypotheses can co-occur and influence each other. Using reindeer (Rangifer tarandus) as a model species, behavioural observations were collected in the field in 2012 and 2013. Allosuckling and allonursing were common in reindeer, and most mothers allonursed and most calves allosuckled. Reindeer calves stole milk, and mothers discriminated their offspring from the offspring of others. Mothers exchanged allonursing at the group level and at the dyadic level, which supported the reciprocity hypothesis. Mothers did not allonurse while their offspring was still attempting to allosuckle, which did not support the milk evacuation hypothesis. Percentage of mass gain and mass at the end of the study increased as the number of allosuckling bouts increased, and allosuckling was not influenced by low birth mass or measures of insufficient maternal milk supply, which supported the improved nutrition hypothesis but not the compensation hypothesis. Mothers in the closely related group allonursed more often than mothers in the distantly related group, which supported the kin-selection hypothesis at the extremes of genetic relatedness. Given that we initially did not find an effect of genetic relatedness, we suggest that kin-selection alone is not sufficient to explain alloparental care. My thesis provides evidence that allonursing contributions detected can depend upon the research design, and we suggest that the indirect fitness benefits of alloparental care may have been overestimated. The evolution of allonursing in reindeer may have originated from inclusive fitness, but the results of my thesis demonstrate that the direct fitness benefits of milk-theft, reciprocal allonursing and improved nutrition and mass gain maintain allonursing in reindeer

Assessment of help value affects reciprocation in Norway rats.

Wild-type Norway rats reciprocate help received in a well-replicated experimental food-giving task, but the criteria to appraise the received help's value are unclear. We tested whether quality or quantity of received help is more important when deciding to return help, and whether partner familiarity and own current need affect this evaluation. We experimentally varied recipients of help's hunger state, and familiar or unfamiliar partners provided either higher caloric food (enhanced quantity; carrots) or food higher in protein and fat (enhanced quality; cheese). Reciprocation of received help was our criterion for the rats' value assessment. Familiarity, food type and hunger state interacted and affected help returned by rats. Rats returned less help to familiar partners than to unfamiliar partners. With unfamiliar partners, rats returned more help to partners that had donated preferred food (cheese) than to partners that had donated less preferred food (carrots), and they returned help earlier if they were satiated and had received cheese. With familiar partners, food-deprived rats that had received cheese returned more help than satiated rats that had received carrots. Our results suggest that Norway rats assess the received help's value based on its quality, their current need and partner familiarity before reciprocating received help

Evidence suggesting that reindeer mothers allonurse according to the direct reciprocity and generalized reciprocity decision rules.

Allonursing is the nursing of the offspring of other mothers. Cooperation is an emergent property of evolved decision rules. Cooperation can be explained by at least three evolved decision rules: 1) direct reciprocity, i.e. help someone who previously helped you, 2) kin discrimination, i.e. preferentially direct help to kin than to non-kin, and 3) generalized reciprocity, i.e. help anyone if helped by someone. We assessed if semi-domesticated reindeer, Rangifer tarandus, mothers allonursed according to the decision rules of direct reciprocity, generalized reciprocity and kin discrimination over 2 years. To assess if reindeer mothers allonursed according to the direct reciprocity decision rule, we predicted that mothers should give more help to those who previously helped them more often. To assess if reindeer mothers allonursed according to the kin discrimination decision rule, we predicted that help given should increase as pairwise genetic relatedness increased. To assess if reindeer mothers allonursed according to the generalized reciprocity decision rule, we predicted that the overall number of help given by reindeer mothers should increase as the overall number of help received by reindeer mothers increased. The number of help given i) increased as the number of help received from the same partner increased in the 2012 group but not in both 2013 groups, ii) was not influenced by relatedness, and iii) was not influenced by an interaction between the number of help received from the same partner and relatedness. iv) The overall number of help given increased as the overall number of help received increased. The results did not support the prediction that reindeer mothers allonursed according to the kin discrimination decision rule. The results suggest that reindeer mothers may allonurse according to the direct reciprocity and generalized reciprocity decision rules

Allosuckling in reindeer (Rangifer tarandus): A test of the improved nutrition and compensation hypotheses

The hypothesized causes and functions of allosuckling can co-occur and influence each other (i.e., non-mutually exclusive). In our two previous studies of allosuckling in reindeer, Rangifer tarandus, the milk-theft and reciprocity hypotheses were supported; the mismothering hypothesis received partial support; and the kin-selection hypothesis was not supported. In this study we investigated: the compensation hypothesis, stating that offspring may allosuckle to compensate for low birth mass, insufficient maternal milk supply (i.e., high maternal rejection rates, low mass of mothers and a large number of allonursing bouts performed by a calf's mother) or inadequate growth; and the improved nutrition hypothesis, stating that offspring improve their nutrition, and hence mass gain, by ingestion of non-maternal milk in addition to maternal milk. For the compensation hypothesis, we predicted that: (1) the cumulative number of allosuckling bouts performed by a calf (hereafter, number of allosuckling bouts) would increase due to low birth mass of calves and other measures of insufficient maternal milk supply; (2) the percentage of mass gain would not be related to the number of allosuckling bouts (i.e., calves that allosuckled often would have the same percentage of mass gain as calves that allosuckled less often) or would have a negative relationship with the number of allosuckling bouts (i.e., calves that allosuckled often would have a lower percentage of mass gain than calves that allosuckled less often); and (3) a negative relationship between the percentage of mass gain and the number of allosuckling bouts would vary with birth mass. For the improved nutrition hypothesis, we predicted that the percentage of mass gain of calves that allosuckled often would increase more than for calves that allosuckled less often. We tested the compensation and improved nutrition hypotheses on 25 mother-calf pairs of semi-domesticated reindeer from parturition to 67 days of age of calves. The number of allosuckling bouts was not influenced by low birth mass of calves or other measures of insufficient maternal milk supply. Percentage of mass gain increased as the number of allosuckling bouts increased. Calves born heavier had a lower percentage of mass gain than calves born lighter. The relationship between percentage of mass gain and number of allosuckling bouts did not vary with birth mass. Our findings did not support the compensation hypothesis. Our results suggest that allosuckling functioned to improve nutrition by ingesting non-maternal milk in addition to maternal milk, which increased the percentage of mass gain. (C) 2015 Deutsche Gesellschaft fur Saugetierkunde.201

Using Geographic Distance as a Potential Proxy for Help in the Assessment of the Grandmother Hypothesis

Life-history theory predicts that selection could favor the decoupling of somatic and reproductive senescence if post-reproductive lifespan (PRLS)provides additional indirect fitness benefits [1, 2]. The grandmother hypothesis proposes that pro-longed PRLS evolved because post-reproductive grandmothers gain inclusive fitness benefits by helping their daughters and grandchildren [3, 4]. Because most historical human data do not report direct evidence of help, we hypothesized that geographic distance between individuals may be inversely related to their capacity to help. Using an exceptionally detailed dataset of pre-industrial French settlers in the St. Lawrence Valley during the 17th and 18th centuries, we assessed the potential for grandmothers to improve their inclusive fitness by helping their descendants, and we evaluated how this effect varied with geographic distance,ranging between 0 and 325 km, while accounting for potential familial genetic and environmental effects[5–9]. Grandmothers (F0) who were alive allowed their daughters (F1) to increase their number of offspring (F2) born by 2.1 and to increase their number of offspring surviving to 15 years of age by 1.1compared to when grandmothers were dead. How-ever, the age at first reproduction was not influenced by the life status (alive or dead) of grandmothers. As geographic distance increased, the number of offspring born and lifetime reproductive success decreased, while the age at first reproduction increased, despite the grandmother being alive in these analyses. Our study suggests that geographic proximity has the potential to modulate inclusive fitness, supporting the grandmother hypothesis,and to contribute to our understanding of the evolution of PRLS