Darwin's vexing contrivance: a new hypothesis for why some flowers have two kinds of anther

Heteranthery, the presence of two or more anther types in the same flower, is taxonomically widespread among bee-pollinated angiosperms, yet has puzzled botanists since Darwin. We test two competing hypotheses for its evolution: the long-standing ‘division of labour' hypothesis, which posits that some anthers are specialized as food rewards for bees whereas others are specialized for surreptitious pollination, and our new hypothesis that heteranthery is a way to gradually release pollen that maximizes pollen delivery. We examine the evolution of heteranthery and associated traits across the genus Clarkia (Onagraceae) and study plant–pollinator interactions in two heterantherous Clarkia species. Across species, heteranthery is associated with bee pollination, delayed dehiscence and colour crypsis of one anther whorl, and movement of that anther whorl upon dehiscence. Our mechanistic studies in heterantherous species show that bees notice, forage on and export pollen from each anther whorl when it is dehiscing, and that heteranthery promotes pollen export. We find no support for division of labour, but multifarious evidence that heteranthery is a mechanism for gradual pollen presentation that probably evolved through indirect male–male competition for siring success.

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The cost of fidelity: foraging oligolectic bees gather huge amounts of pollen in a highly specialized cactus–pollinator association

Biological Journal of the Linnean Society ◽

10.1093/biolinnean/blz083 ◽

2019 ◽

Vol 128 (1) ◽

pp. 30-43 ◽

Cited By ~ 2

Author(s):

Isabelle Cerceau ◽

Samuel Siriani-Oliveira ◽

Ana Laura Dutra ◽

Reisla Oliveira ◽

Clemens Schlindwein

Keyword(s):

Male Reproductive Success ◽

Flower Opening ◽

Mechanical Filter ◽

Pollen Presentation ◽

Oligolectic Bees ◽

The Cost ◽

Fruit And Seed Set ◽

Flower Handling ◽

Plant Pollinator ◽

Pollinator Foraging Behaviour

Abstract Plant–pollinator interactions vary along a specialization–generalization continuum. Advances in understanding the evolutionary and ecological consequences of different degrees of specialization depend on precise data on plant–pollinator interdependency. We studied the association of Parodia neohorstii (Cactaceae) and its bee pollinators focusing on pollinator foraging behaviour, flower functioning, female and male reproductive success, and pollen fate. Parodia neohorstii showed synchronized flower opening and pollen presentation but discontinuous blooming. The apparently generalized flowers partition pollen through thigmonastic stamen movements that function as a mechanical filter against generalist bees by restricting access to the major pollen reservoir to bees that show flower handling ‘know-how’, thereby favouring the oligolectic bee Arhysosage cactorum. This pollinator adjusted its pollen foraging to flower opening, removed pollen hurriedly, and promoted maximal fruit and seed set, which was minimal in its absence. Estimates of pollen fate revealed that a huge amount of pollen flows to specialized pollinators (86.5%), and only 0.9% reaches conspecific stigmas. The specialized interaction between P. neohorstii and Arhysosage cactorum, both threatened species, is efficient but fragile. Any environmental modification that causes a mismatch between the partners is likely to result in reproductive failure.

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The dimensions of species diversity

10.1101/400481 ◽

2018 ◽

Author(s):

Matthew J. Larcombe ◽

Gregory J. Jordan ◽

David Bryant ◽

Steven I. Higgins

Keyword(s):

Species Diversity ◽

Ecological Niches ◽

Niche Evolution ◽

Niche Space ◽

Niche Modelling ◽

Ecological Opportunity ◽

Competing Hypotheses ◽

Niche Competition ◽

New Hypothesis ◽

Lineage Diversification

ABSTRACTDiversification processes underpin the patterns of species diversity that fascinate biologists. Two competing hypotheses disagree about the effect of competition on these processes. The bounded hypothesis suggests that species diversity is limited (bounded) by competition between species for finite niche space, while the unbounded hypothesis proposes that evolution and ecological opportunity associated with speciation, render competition unimportant. We use phylogenetically structured niche modelling, to show that processes consistent with both these diversification models have driven species accumulation in conifers. In agreement with the bounded hypothesis, niche competition constrained diversification, and in line with the unbounded hypothesis, niche evolution and partitioning promoted diversification. We then analyse niche traits to show that these diversification enhancing and inhibiting processes can occur simultaneously on different niche dimensions. Together these results suggests a new hypothesis for lineage diversification based on the multi-dimensional nature of ecological niches that accommodates both bounded and unbounded diversification processes.

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Echoes of Latifundism? Electoral Constituencies of Successor Parties in Post-Communist Countries

East European Politics and Societies and Cultures ◽

10.1177/0888325403258286 ◽

2004 ◽

Vol 18 (1) ◽

pp. 10-44 ◽

Cited By ~ 10

Author(s):

Jacek Lubecki

Keyword(s):

Economic Status ◽

East Germany ◽

Regional Level ◽

Average Level ◽

Socio Economic Status ◽

Competing Hypotheses ◽

Social Advancement ◽

Communist Countries ◽

New Hypothesis ◽

Regional Variance

This article examines patterns of elector support for successor parties in Hungary, Poland, East Germany, and Russia. After consideration of competing hypotheses purporting to explain variance in successor vote, the author proposes a new hypothesis—that regions dominated by latifundism in pre-communist times, and where masses of agricultural proletarians and impoverished peasants experienced the communist period as an era of unprecedented social advancement, show an above-average level of elector support for successor parties. This hypothesis is tested on a regional level in the four country-cases and found to be valid and a more powerful determinate of regional variance in patterns of successor vote than socio-economic status of regions in the post-communist era.

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The specialization–generalization continuum in oil-bee pollination systems: a case study of six Brazilian species of Tigridieae (Iridaceae)

Biological Journal of the Linnean Society ◽

10.1093/biolinnean/blz185 ◽

2020 ◽

Vol 129 (3) ◽

pp. 701-716

Author(s):

Suiane Santos Oleques ◽

Jefferson Nunes Radaeski ◽

Soraia Bauerman ◽

Olivier Chauveau ◽

Tatiana Teixeira de Souza-Chies

Keyword(s):

Reproductive Biology ◽

Significant Contribution ◽

South American ◽

Bee Pollination ◽

South American Species ◽

Pollinator Behaviour ◽

Visitation Frequency ◽

Pollination Systems ◽

Plant Pollinator

Abstract Several South American species of Iridaceae, especially those of Tigridieae, produce floral oils as rewards to oil-bee pollinators. The present study aimed to contribute to a deeper understanding of the reproductive biology, pollination ecology and level of specialization of the interactions of species encompassed in Tigridieae. Data on breeding and pollination systems were acquired from six species native to Southern Brazil. The visitation frequency and pollen load of pollen- and oil-collecting bees were also investigated. The results strongly suggest that the studied species are distributed along a specialization–generalization continuum. Three oil-producing taxa, Cypella herbertii, Cypella pusilla and Cypella amplimaculata, were pollinated effectively by oil-bees, whereas in the other two studied species, Kelissa brasiliensis and Herbertia pulchella, the oil-bees appeared to function as oil thieves, owing to failure to contact the plant reproductive parts during oil-foraging behaviour. New insights into aspects of the specialization–generalization continuum of pollination systems, differences in pollinator behaviour during oil and pollen foraging, and reproductive outputs of the studied species are provided. Taken together, our results provide a significant contribution towards a better understanding of reproductive biology and plant–pollinator interactions between Iridaceae and oil-collecting bees.

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The evolutionary history of division of labour

Proceedings of The Royal Society B Biological Sciences ◽

10.1098/rspb.2011.0766 ◽

2011 ◽

Vol 279 (1726) ◽

pp. 116-121 ◽

Cited By ~ 46

Author(s):

Carl Simpson

Keyword(s):

Basic Feature ◽

Cell Types ◽

Division Of Labour ◽

Functional Specialization ◽

Evolutionary Origins ◽

Social Animals ◽

History Of ◽

The Many ◽

Internal Variation ◽

New Hypothesis

Functional specialization, or division of labour (DOL), of parts within organisms and colonies is common in most multi-cellular, colonial and social organisms, but it is far from ubiquitous. Several mechanisms have been proposed to explain the evolutionary origins of DOL; the basic feature common to all of them is that functional differences can arise easily. These mechanisms cannot explain the many groups of colonial and social animals that exhibit no DOL despite up to 500 million years of evolution. Here, I propose a new hypothesis, based on a multi-level selection theory, which predicts that a reproductive DOL is required to evolve prior to subsequent functional specialization. I test this hypothesis using a dataset consisting of the type of DOL for living and extinct colonial and social animals. The frequency distribution of DOL and the sequence of its acquisition confirm that reproductive specialization evolves prior to functional specialization. A corollary of this hypothesis is observed in colonial, social and also within multi-cellular organisms; those species without a reproductive DOL have a smaller range of internal variation, in terms of the number of polymorphs or cell types, than species with a reproductive DOL.

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