Spots and manes: the curious case of foster care between two competing felids

Abstract

Adoption of unrelated young can have detrimental consequences to the caregivers’ fitness in the form of costs emanating from maladaptive altruism. Owing to such costs, complete adoptions and allo‐nursing are relatively rare in the animal world, more so between species that compete with one another. Lions and leopards compete through both exploitative and interference mechanisms, resulting in profound aggression and suppression at mutual encounters. Through intensive monitoring, we provide a detailed and prolonged account of a complete adoption of a leopard cub by a free‐ranging Asiatic lioness. We briefly review existing literature on foster care in the animal world and suggest that maternal instincts and inexperience, coupled with behavioral and physical resemblance between lion and leopard cubs, could have acted as proximate cues in initiating such an unprecedented association. Furthermore, the unique sociobiology of Asiatic lions wherein the sexes live separately in small groups likely favored the duration of this interaction (~45 d). We also discuss and speculate about broader perspectives of offspring recognition in the animal world and ask whether the study of such important yet rare associations has implications for our understanding of parental care.

Introduction

Complete adoption and allo‐nursing are viewed as excessive forms of alloparental care that challenge evolutionary concepts built around the “selfish gene” that in turn directs individuals to propagate their own genes often at the cost of another's (Dawkins 1976, Carzon et al. 2019). Nursing unrelated offspring can be energetically costly with detrimental consequences to the donors’ inclusive fitness. Generally, adoption and allo‐nursing entail a high degree of parental investment in the form of time, energy, and milk/food offered to raise “someone else's genes.” Such instances are thus evolutionarily mainstreamed when costs of raising unrelated young are ameliorated through kin selection (e.g., in lions where females in a pride nurse each other's cubs because all the lionesses are matrilineally related, Packer et al. 1991) or such acts directly help in boosting the donors’ lifetime reproductive success (e.g., cheetah Acinonyx jubatus mothers have been reported to adopt additional orphaned male cubs that ultimately help their own male cubs to forge large coalitions in adulthood and have better ability to hold territories and sire young, compared to when alone or in small coalitions, Gottelli et al. 2007). Besides such evolutionary causes, nonadaptive “reproductive errors” have also been posed as explanations for allo‐nursing, wherein a mother's inexperience and/or proximate fidelity to young might have caused her/them to adopt unrelated infants (e.g., in the case of northern elephant seals Mirounga angustirostris, pups often get separated from their mothers in densely crowded beaches and some of these estranged but lactating mothers adopt unrelated orphans; Riedman and LeBoeuf 1982).

Almost all such adoption instances are intraspecific, barring two exceptions in the wild: (1) A young marmoset Callithrix jacchus was adopted by a family of anthropogenically provisioned capuchin monkeys Cebus libidinosus (Izar et al. 2006) and (2) a bottlenose dolphin Tursiops truncatus nursed a melon‐headed whale calf Peponocephala electra alongside her own calf (Carzon et al. 2019). In these cases, none of the foster parents and adoptees however belonged to mutually competing species. Strongly competing species exhibiting instances of foster care is ostensibly less likely because of the additional costs (of competition) involved. Lions and leopards, by the virtue of having similar resource needs, are known to severely compete with each other and are often hostile at mutual encounters (Caro and Stoner 2003). Lions kill adult leopards and their cubs (Palomares and Caro 1999; S. Chakrabarti, personal observation), steal their kills (Chakrabarti and Jhala 2019), while leopards attack and/or kill unguarded lion cubs (Schaller 1972).

Contrary to the accepted understanding of lion–leopard interactions, in December 2018, we came across an adult free‐ranging Asiatic lioness (Panthera leo persica) taking care of a leopard cub (P. pardus fusca) in addition to her own young cubs in the Gir forests of Gujarat, Western India (Fig. 1A). Over the course of the next one and a half months, we intimately monitored this lioness that was recorded to nurse the leopard cub and rear it as her own (Fig. 2). The leopard cub (a male of ~2 months with characteristic blue haze in its eyes that indicated its very young age; Fig. 1B) was always found to be associated with the lioness: suckling from her, feeding from kills that she made, and playing with its foster siblings (Fig. 2). The prolonged duration and the ecological context of the observed foster care between these two sympatric and competing felids are bizarre and stimulate intriguing behavioral questions.

Figure 1

(A) The leopard cub with its foster family of an Asiatic lioness and her young cubs (in this picture, only one lion cub out of the two is visible) in Gir, Gujarat, India. (B) The blue haze in the eyes of the leopard cub indicates its very young age (~2 months). Photo credit: Dheeraj Mittal.

Figure 2

A panel of images showing the unusual adoption of a leopard cub by an Asiatic lioness in Gir, India. The images depict various behavioral events of this association, for example, (A–C) the lioness accompanying and nursing the leopard cub; (D, E) the leopard cub playing with its foster siblings (note the size difference between cubs of the two species which are almost of equal age); and (F) lioness sharing her kill with the adopted leopard cub. Photo credit: Dheeraj Mittal.

Observations and Perspectives

Free‐ranging Asiatic lions are currently distributed as a single relic population in the Gir Protected Area (Gir PA), a semiarid deciduous forest covering ~1800 km² with teak Tectona grandis, Acacia spp., and Zizyphus spp. as the major vegetation, and the adjoining human‐dominated Saurashtra landscape of about 12,000 km² in western India. The Gir landscape has a history of monitoring wildlife and their habitats to an extent that PA managers and trackers intensively patrol the entire landscape, tailing and systematically checking each individual lion (Divyabhanusinh 2005). Such monitoring has also aided scientific research on lions in the form of one of the longest carnivore research projects in Asia (Jhala et al. 2019).

Owing to DM, SC, and SK's first‐hand association with the study area in the capacities of park managers (DM and SK) and field researcher (SC), we could keenly observe this atypical behavior and consider prior contextual information. Furthermore, the lioness in context belonged to a pride that has been intensively monitored (adult females were detected at least once every 5 d for documenting behavior and cub survival; Chakrabarti and Jhala 2019) between 2012 and 2018. This allowed us to explore the rationale of this association at the backdrop of her reproductive history. In the course of 45 d, we could directly observe the leopard cub along with its foster family for 29 d (Appendix S1), often with multiple detections on the same day. Camera traps were also deployed at a waterhole frequented by the lioness and her cubs. The detections spanned across 2.6 km² (Fig. 3), a relatively small area compared with an adult lioness’ home range (~35 km²; Jhala et al. 2009). The lioness was clearly restricted in her forays because she had young cubs that were less mobile, especially the leopard cub. However, this interesting interaction ended when we discovered the carcass of the leopard cub near a waterhole on 11 February 2019. A subsequent autopsy carried out by the field veterinarian revealed that the cub was suffering from congenital femoral hernia which could have resulted in its death. No injury marks were found on the body of the leopard cub carcass.

Figure 3

Maps showing (A) relative position of Gujarat in India; (B) Gir Protected Area (PA) in Gujarat; and (C) observed locations of the leopard cub along with its foster family of an Asiatic lioness and her two cubs at the edge of the Gir PA. The observed locations are just outside the boundary of the Gir PA, but within the adjoining forest matrix that is managed as part of the Gir PA network.

While there happens to be one other instance where an African lioness (which had recently lost her cubs) was observed with a leopard cub in the Ndutu area of Ngorongoro in 2017 (https://www.nationalgeographic.com/news/2017/07/leopards-lions-cubs-nursing-tanzania/), the association lasted only for a day and was not considered as a formal adoption (I. Jansson, personal communication). From our prolonged observations, it is unlikely the interaction that we report herein was due to a “momentary” confusion in recognition from the lioness, but rather might be a result of a deeper behavioral response that continued for a long duration and qualifies as a formal adoption. Such a response might have been elicited because the lioness was young (5‐6 yr of age characterized by a pinkish nose pad with off‐white canines and negligible jaw slack; Fig. 2A; see Jhala et al. 2019 for aging criteria of Asiatic lions) and somewhat inexperienced (this was her second litter, her first litter of two cubs died at a very young age). Also, given that she was a lactating mother with cubs of her own, her maternal and hormonal instincts could have overridden her recognition or the lack thereof for an “unusually spotted cub” (Video S1). Our arguments follow similar observations of nonadaptive adoptions reported for primates (Thierry and Anderson 1986).

But how did the leopard cub become an orphan in the first place? To that, we can only speculate from additional observations. A day after our first detection of the leopard cub with its foster lion family, we spotted an old female leopard at the same location (Appendix S1). Although we could not assess the lactating state of this leopardess, it is possible that she was the biological mother of the orphaned cub. The leopard cub, which we now know had congenital femoral hernia, might have been abandoned by the old leopardess and was subsequently adopted by the lioness that happened to be in the area, feeding on a nilgai Boselaphus tragocamelaus kill. From long‐term demography data, we know that Asiatic lionesses live in smaller groups than their African conspecifics (average female group size ~ 2 adults), and adult males and females largely segregate from each other, interacting primarily for procreation (Chakrabarti and Jhala 2019). Furthermore, lion females are often on their own in the first few months after giving birth. We believe that the distinct sociobiology of Asiatic lions coupled with the reproductive state of the lioness facilitated the absence of other adult lions around her immediate vicinity, which otherwise would possibly have recognized and killed an alien cub. This association also likely indicates that the proximate cues from cubs such as sounds, body postures, begging for milk, and the presence of spots (lion cubs have prominent leopard like spots on their foreheads and the underside of limbs and bellies) that evoke “mothering” tendencies might be similar across lions and leopards. Maternal care seems to be instinctive and follow fixed action patterns (Lorenz 1982), honed to better suit natural selection through age and experience. Our observations appear akin to precursive mechanisms underlying brood parasitism (Payne 1977) that favor instinctive parental care over offspring recognition. Although such adoption instances are rare, we urge researchers to consolidate similar observations across taxa to examine whether such foster care generally occurs between species that resemble each other when young and/or are related. While speculative, this might provide valuable understanding of the evolution of parental care and offspring recognition in mammals.

Acknowledgments

We thank Sunil Berwal, Lalit Vara, Tushar Limbadiya, Dilipkumar Sisodiya, Ramkubhai, and Vanrajbhai for their dedicated field skills, keen recording of this incident, and sharing of information. We thank Craig Packer for providing insights. We also thank Ingela Jansson for sharing comprehensive information about the lioness–leopard association from Ndutu, Ngorongoro. We thank the Wildlife Institute of India for its support. Indranil Mondal is thanked for his help with the map. Special thanks to Andrew J. Matthews and Academic Technology Support Services at the University of Minnesota. We thank Mayank Kohli and Aamod Zambre for constructive comments on an earlier version of the manuscript. DM and SBK collected field data on the association; SC provided information on the lioness and her life history; SC, DM, and JKB conceptualized the paper; SC, JKB, and DM wrote the manuscript. DM and SC contributed equally to this work. All authors read and commented on the manuscript drafts. We declare that there is no conflict of interest associated with this research and its submission.